I've heard higher levels mean more enemies, but I figure if I get my level high enough, it wouldn't really matter after a while.
The problem isn't so much the difficulty, but rather the tedium. Fighting 100+ enemies every battle does get old after a while, especially since the only spells capable of hitting more than 10 enemies either only work outdoors or only work against undead.
Winning most large battles isn't that hard if your characters are fast enough to act before the enemy; turn off the sound before hand (the sound slows combat down, as it has to play before the battle can continue, which is annoying when there are 100+ enemies that need to die), cast Power Shield (makes you lose less HP when you take damage), and just Ctrl-A (IIRC) to auto-battle; as long as the enemies are vulnerable to physical attacks and don't have absurd HP totals, you will win the battle after a while. Now, if the game decides to spawn something like 100+ Orc Gods (50,000 HP each), then you will likely want to run away and hope the game gives you a more reasonable encounter when you return to that position.
There is also an option you can change that affects the number of enemies per encounter; as you reach higher levels, you will want to change that.
Note that fixed encounters (those with a fixed group of enemies) are not affected by any of this.