I prefer the Warhammer Fantasy approach: if you can use magic, it's at will as many times as you want it, but it can fail and, more importantly, backfire spectacularly.

Also, that DnD5 made cantrips scale up in power with player level is something I enjoyed at first, but the more I think about it, the less I like it. Especially when you can make a whatever 19 / warlock 1 and throw 4x 1d10 attacks at very long range at will.