There are basically two versions of the HR I was contemplating. But the crux of the matter is that I believe that the requirements for Potent Spells overall make the virtue non-competitive as a choice compared to other options at the same grade of virtue/investment. The extra time and thus xp costs involved in making the virtue work are completely seamless/transparent when compared to say a Magical Focus.
- Option 1 - Remove Potent Spells
This would make it so the bonus (S&M) is applicable to any spell in the category of the virtue to which the user has appropriate casting tools. The bonus is still capped by Magic Theory. This thus provides the same possible bonus from the virtue just without the extra burden of Potent Spells being required.
Potent Spells then don't exist and can't be learned by others, and thus the virtue only provides bonuses to someone who has it.
- Option 2 - Potent Spells Are Generic
This would be as @Nithyn indicated, that Potent Spells are one and done. Having a potent version then lets you use casting tools to provide bonuses to the spell as usual but the casting tools aren't set and can evolve over time to get bonuses up to your Magic Theory.
This means Potent Spells exist however it begs the question whether said spells should be usable by others.
One reason I dislike Option 2 is it seems unspecified whether, for instance, Spell Mastery should be transferable to being used with an equivalent Potent Spell. If not then this is another reason why Potent Magic fails in comparison with other options and ends up being so rarely taken and used in play.
For a great deal more discussion on the topic, including people who disagree with me, the thread I mentioned is here: