There’s a lot to be said for the fairly limited number of spells as in, e.g., Rebel Mini’s MIGHTY ARMIES. (Or, on a tactical level, SONG OF BLADES AND HEROES)
Otoh, lots of us enjoy fiddling with spell lists and minimaxing with points systems and such. Depends of whether your prime pleasure is planning a game or actually PLAYING it! (Playing is obviously the desired end, but lots of us spend far more planning, willingly or not. How many hours of faculty meetings have I whiled away with army lists?!?)
In PRIDE OF LIONS magic can be quite important, though rarely decisive. It is the equivalent of, say, electronic warfare plus off-the-board artillery. Leadership (issuing orders, motivating troops, rallying routers, etc.) is at leasat as important, and the battle is usually decided by the clash of rival battle lines. As it should be.
But the magic system CAN be complex enough to be a sub-game in its own right, if players want to do it that way. One mid-level mage per side means a small impact on the outcome, particularly since the rival mages will often cancel out.
But give each side several mages, working from more than one spell list and with varying levels of power, and 1) the game slows down; 2) the magic battle becomes a separate “game”; and 3) magic may decide who wins.
Or maybe not; there’s the old Cold War joke: what do two Soviet tank generals say to each other when they meet in Paris? Answer: “Hey, I wonder who won the air war?”