Benjamin Olson
Hero
The main "balance problem" between martials and casters is not the power of high level spells, it is that martials are geared primarily towards doing at will single target damage really well, with everything else secondary. You may find a build or subclass that substantially emphasizes something else, but basically single target damage is backed in as goal one for martials. Meanwhile casters can be built to specialize in numerous other things. A lack of high level spells doesn't really address this.
At every table I've ever played at the magicians are using their spells to try to get the fire lizard where the martial character can slay him. That's the basic teamwork dynamic the game assumes.Now get over there and pretend to be a threat to that 50' long magical fire lizard while I cast a trivial spell to do everything you cant!