It depends on what you’re trying to do. If you spam abilities, you will run out of mana.
Mana Potions used to be the way you used (instant) and mana was irrelevant, because when you ran out of mana you could just spam mana potions. So we redesigned them to recover mana over time. This way mana & mana recovery makes more sense, and it also gives Elven Elder & Shillien Elder classes a place in the game (with their mana recharge ability). I’m working on a possible buff to those classes, perhaps AoE mana recharge or buff that recharges more mana over time, as well as a possible mana recharge item which requires you to sit down so you can replenish your mana.
But I don’t think increasing mana over time on the current mana potions makes sense. Don’t forget that mana is a resource, if you have unlimited mana there’s no point in having it in the first place.