Howdy! In playtest I've tried 3 MP per wizard level and it is not gamebreaking.
On the other hand a 'bolt' at level 1 could deal 15 damage (or 30 of a status effect) to up to 10 targets in a straight line.
It exists to emulate Lightning Bolt with is a 3rd level spell you obtain at level 5 in either oldschool D&D and 5E.
In FTW by level 3 you could use it spending 5 MP (almost all your magic) but by level 5 you could cast it and have 5 MP for other spells or to cast it again.
Hope this context helps and I look forward to people launching ice bolts, sleep bolts and other weird combinations using the mix and match spells and spellshapes.
Edit: also this game is far from done and feedback and questions will shape the design.