That being said: a lvl 75 effect to create a living body seems...excessive. The CrAn guidelines ramp up from 5 (create insect) to 10 (fish) to 15 (mammal). So, add +1 to complexity and switch over to CrCo, and I'd call it a base 20 effect.
Of course, if this is an issue of magic trying to do something that the Divine considers its own bailiwick, then I understand - but it seems different to "create completely new body" than "resurrect old one". However, maybe the idea was that they didn't want it to be too easy to create a completely new and living copy of an old and dead body - which is functionally identical to the lvl 75 resurrection idea. The only difference between the two is that with a copy, you're left with the original corpse, whereas with a normal resurrection, you aren't. So maybe there's something to having it be that difficult.
There's always the old-school method of creating a body: get a convenient target pregnant, then use CrCo to hurry the effect along. More fully laid out in the Fertility Magic section of...Ancient Magic(?). And at the end of the day, you'd have a soul in that new body.
Of course, if you used MuCo to make an otherwise infertile target fertile, the Limit of Essential Nature may prevent a soul from being attached to the new body - or it may simply prevent a pregnancy from actually occurring. Personally, I'd go for the soulless abomination route - simply because it makes for a more interesting story.
Then there's always the Golem option - which counts as "no soul, but has a spirit". But that's back in with the Divine, and suggests that creating a living, human-like entity isn't nearly as easy as it sounds.
It's a base 5 effect to create a corpse. It's a base 70 effect to raise the dead. It's arguable whether the spell that raises the dead would even work on a created corpse, since it was never alive to begin with.
A base 5 Creo Corpus effect combined with a base 10 Rego Corpus can animate a body.
Keep in mind that with the level 75 spell the idea is implicitly not just to reanimate the corpse but to put the person's soul (or something resembling it) back into the corpse.
With a created body such as I have suggested the idea is to create a body without a mind or soul that the magus could move into. Functionally before moving in it is not much different than a corpse aside from the fact it ages and requires maintenance (and smells better after 3 days)
Another good reason that wasn't mentioned (callen mentioned the specialist) is that if you are doing the LR yourself, it's a lab activity and the vis limit is MTx2. Since the cost in vis is Age/5, rounded up, someone who is 41-50 must have a MT score of 5 to be able to handle the 9 or 10 pawns of vis necessary for the ritual. That's not necessarily a hard thing to acquire, but...
I have a Corpus specialist who was already 37 when he was a magus, and his MT at gauntlet was only 3 (4, with Corpus) and
I was under the impression (I'll freely admit that it could be wrongly) that, since the design of the ritual did not consume any Vis, the limit of MTx2 did not come into play. The "consumption" of the ritual takes a trivial amount of time compared to a season, but that is the only point where Vis is consumed, so it should not interact to seasonal limits on Vis.
Magic Theory applies for the the first use of a longevity ritual, because it is a seasonal activity made in a lab, which results in the longevity ritual. If one didn't limit the amount of vis used based on Magic Theory, then one could add as much vis as they wanted or had to make the ritual as powerful as they wanted. It isn't explicitly stated that there is a limit in the Longevity Ritual section in the Laboratory chapter that there is any limit for the amount of vis used. But it does say that the season spent designing the ritual culminates in a focus for the magus to use to maintain his longevity, that is something is made during that season, something that used or consumed vis.
If the longevity ritual fails at a later date and it needs to be reperformed, then the amount of vis used at that later time is governed by the Art score of the types of vis used in the longevity ritual when it was first designed + any vis necessary due to increased age. Again, this isn't explicitly stated anywhere, and it doesn't even specifically match the situation of using vis in spell casting discussed on page 82.
By your argument, the slippery slope is that there are no explicit limits on how much vis may be used in a longevity ritual, ever. I think it's reasonable that the first longevity ritual designed is limited by Magic Theory, and any subsequent reperformance of that ritual is governed by the Art limit. With no limits, no magus should have ever died, unless they were vis poor.
Hmm good point, I suppose I'd never really encountered that as the campaigns I've been in give between 1-2 pawns per magus per year, so there would not be that problem you stated.
I'm pretty sure that not only is Jonathan Link correct but also that these are both stated explicitly in one of the later books. It was not written in ArM5 in any explicit way. There were a lot of questions. I think I was in the spell-casting camp after examining it more carefully, having originally been in the laboratory camp; others were in the laboratory camp; and then others were split (as it turns out to be and Jonathan Link explained above) as laboratory the first time and spell-casting at later times. Then it was addressed more explicitly. I believe there is a box/sidebar in one of the earlier books that addresses this, though I don't remember which book. It could be something like TMRE that has some things that relate to longevity rituals within it. I would have to spend some time digging...
