I've noticed in the Harry Potter series that the most powerful spells ever mentioned never go beyond killing, blowing up a few feet, or knocking someone out. Grindelwald's control of lightning in Fantastic Beasts: The Secrets of Dumbledore is the only spell I find to be slightly more destructive (because of the lightning). Even Wormtail's spell that killed 13 Muggles was aimed at something else that catapulted the number of deaths up.
I've been wondering if the strength of the spells has to do with the wand power or the wizard's skills - since the Elder Wand seems to be a factor in Grindelwald's control of the lightning.
Is there a canon answer for the limit to how strong spells can be and [if there is a limit] what factors make it the limit?
Anything approved by JKR is considered canon by me.