I get the “mana is important” idea as a whole, but…
mana bonuses don’t actually do anything if they don’t get a hero to a checkpoint value where they actually fire at least one tile faster on offense, or half-a-tile (one incoming tile) faster on defense,
Now, admittedly, this gets complicated when one says “well also what kind of mana buffs/debuffs might run at any one time due to Specials etc.” but… +2% mana gen doesn’t generically actually make a hero 2% faster.