Even if you accept my original proposal for changing Parma Magica in toto, it still isn't "balanced." And if the game is clearly and obviously unbalanced in favor of one thing (high penetration) as opposed to another thing (high magic resistance) taking the initiative is fait accompli, and there are no alternative solutions and strategies, merely a race towards the path to supposed victory, or in this case, to always improve penetration. Ignoring Parma is something of an effective strategy, then.
I don't have any sacred cows in this discussion, but it's something I've been ruminating on for a while, but haven't been able to articulate it well. I think ezzelino said it best. Parma Magica is a bit of a wasted ability. I'd like to change that, somehow. I think it does need to change, somehow.
Right, but that comes at the cost of eliminating foci that don't have anything to do with Penetration, and thus don't relate to Parma Magica, at all, wrecking some really interesting foci like MMF Ships or mMF Self-transformation to name but two. I think foci are cool, as an SG and as a player. Eliminating them just for foci which be used to boost penetration seems shortsighted. So maybe I do have a sacred cow or three. In general, I'd like to focus on Parma Magica rather than making it more effective by nerfing something else, because when you go further afield from the problem the risk of unintended consequences increases.
Trying to take this line of thought to its logical conclusion, wouldn't it be possible to keep foci as they are, except that they can never improve penetration beyond what you would have without the focus? So if you had an applicable focus and stamina 0, technique 10, form 10; and used a level 15 effect, that would give a penetration of 5 rather than 15. On the other hand you could cast a level 30 effect without losing fatigue, albeit with -10 in final penetration.
Something that is partly forgotten in this discussion is the mastery ability that doubles magic resistance against similar spells. Anyone with Flawless Magic could invent a lot of small spells in a season and then double magic resistance against all of them. For most magi this might be overkill, for a MR specialist it's not.
Another thing partly forgotten is familiars. I think familiars are a much more plausible way to specialise in magic resistance than parma. Having a powerful familiar can be done without wasting any xp outside your normal specialty, and can give a very high MR. Later it can be fed vis to improve your MR without wasting any seasons in study or practice.
I can understand if some people would prefer the parma itself to be powerful for stylistic reasons. I think that parma as an accelerated ability would be really stylish as a mystery virtue, and probably not unbalanced even as the default.
I think you are perhaps looking at the problem from the wrong side. It isn't so much that Parma Magica is too weak or too difficult to improve. It is rather that high Penetration total are too easy to achieve. Compounding the problem is the fact that Parma is a passive ability -- it doesn't provide the player with something to do that makes it interesting.
Penetration totals can get too high, much too easily. Solve that problem, and Parma gets much more attractive. Perhaps the basic formula to calculate Penetration should be adjusted? For example:
Current formula is Casting Total + Penetration Bonus – Spell Level
Modified formula could be (Casting Total – Spell Level) / 2 + Penetration Bonus
It would make the Penetration ability matter again, while making both supernatural critters' Might-based resistance and Parma Magica stronger.
As for the fact that Parma is a passive ability, well, someone suggested that integrating fast-cast defense might be a good way to go. This would certainly be more attractive to me than simply making Parma stronger across the board.
I'm certainly up for turning Parma Magica into an active component of the player's response. I find Fast Cast defense tends to be complicated and unwieldy at the table (are you quick enough, can you work out what the effect is, now roll for the spell, compare against the spell level...). I like the idea of that Fast Cast simply adding to the MR, but I'd have to see a spread of numbers before I'd commit. For instance, to defend against a spell (no matter how penetrating), you need to hit half that spell's level. That's pretty achievable against a solid level 20 attacking spell/effect. My problems with Fast Casting can be dealt with by getting rid of the check to see if you know what effect you need to cast and maybe by exchanging the quickness check for spending a Fatigue Level or a Confidence Point (we always have those hanging about, right?).
I've read a number of options in this thread and I'm not sure I'd jump from the core mechanic to those, to be honest. I think they have so far tended to require more caveats and exceptions than I'd be prepared to deal with.
Parma Magica is great. I mean, five-X the Ability level and then add a Form? I'd take that in defense against a Might 15 Faerie any day. I'd take my chances. The only problem I have is that the number of modifiers open to casting in order to increase Penetration isn't open to Parma Magica - what if I know the assailant's horoscope, have an effigy of him, possess an arcane connection; all these things should help me ward (lower-case w) against his magic. Then, if all else fails, why not throw some vis in there to boost my MR?
But then, all those options start to apply to Fast Casting too, if only the process wasn't bogged down in too many rolls.
However this thread turns out, we're unlikely to agree on a final definitive Parma rethink.
here's an extreme rethink of Parma: It just works. It defends against any supernatural effect, period. It is not an Ability. If you want to get at a Hermetic magus, you have to do something else.
While I would be on the "No" side of that particular campaign, I do wonder just what kind of Parma Magica score Trianoma had when she went out demonstrating this wondrous magical shield to all and sundry wizards she could find. Did not one of them have a decent Penetration score..?
Remove MMF from Casting Totals, where it's the problem. It's seldom needed for casting the spells (other than to provide stupid amounts of Penetration), more often used for inventing spells or items.
Now that I think of it, having Magical Focus double MAGIC THEORY becomes attractive. It cuts out casting totals entirely but would actually allow the magi with MMF 'Swords' or 'Gems' make greater invested devices without sky-high Magic Theory.
Well, we can assume that Bonisagus was a Great Teacher (he taught a LOT of people) and probably taught Trianoma a lot of Parma. She probably had a Parma of 5-6 before she started out (and in all her travels probably increased it frequently). That might not seem like much, but remember that the founders didn't have large libraries of books to study their magic from, so their arts scores might not have been that high compared to a 'modern' magus of similar age (they didn't have much in the way of Longevity magic either, except for maybe Goerna and I believe Merinita).
Actually, I wanted to suggest something similar, is (only slightly) less extreme. Parma just works, protecting you against a number of supernatural attackers equal to your score. You may protect other characters too; each effectively reduces your Parma score by one. You may count a horde of lesser attackers (say, a dozen pesky imps) as a single attacker; conversely, a powerful attacker (say, Lucifer) may count as two or three.
The problem is that if Parma became too effective (no matter how) people would then start using magic to sling non-magical rocks against magi, open chasms beneath their feet, trap them under a pile of sand etc. The end result is that magi are still vulnerable, but suddenly the palette with which I can paint a threat is much reduced. I'm not 100% sure I'd like that much. This would change if Parma were changed to really block all threats from magic, even "indirect" ones. I'd like that very much.
Magic Resistance is supposed to be penetrable in all cases, albeit with some preparation (arcane and sympathetic connections, or vis) if necessary. However, the fact that weaker spells have higher Penetration is supposed to ensure that a small amount of Magic Resistance is still useful — it stops the opponents using their "instant kill" spells, and so buys you time.
The ArM5 implementation is probably not perfect, but the real and obvious bias in favour of Penetration is deliberate.