I'm not making an RPG, but it is an complaint I have with many Dungeons and Dragons editions. Powerful spells like Anti-Magic Field, Contingency, Wish, etc. don't feel thematic enough to me, just really, really, really powerful. I also wish spellcasters were a bit more flexible in the skill/weapon department, so that when their theme spells weren't applicable they could instead rely on moderate weapon use instead of having a bunch of differently themed spells. Water magic won't work? Time to hang back and fire with a crossbow.