Oh, there are quite a number of reasons:
- CrAn says that to create might creature, you need Vim requisite. First reason why MuCo(An) is not sufficient.
- CrAn again says that you need requisite of the powers (so, if your dragon cast fire, Creo Ignem requisite).
- only adding those requisite allow players to say: with my level 60 spells (base 20 +sun, + 4 requisite) I become might 70. (Which mean 70 MR, so parma 14). Thus you would want to add a cost in the spell for the might. Which? Either the base? (but that doesn't take into account the fact that a big beast is harder to manage than a mouse of virtue) thus you end up with adding levels to the spell, equal to level of might.
Finally you go to this message