the ability to expend low level slots (even by bunching them up) for high level effect is devastating.Three weeks pass. The fighter gets to beg the DM with Mother May I on using skills (something the wizard could do if they bothered). The wizard gets even more flexibility in manipulating the world by eeking out more casts of fabricate or whatever they want to do.
Casters need to be gutted, not given more power, and versatility is power.
I can't imagine someone thinking a 2nd level spell slot +3 1st level spell slots for an extra 5th level spell slot isn't amazing...