The issue I have with this is, cantrips are already oretty limiting. While they can get up to 4 dice in damage, in most cases because it is magic, you don't get to add any modifiers to it. Also you only get 1 attack per round in most cases. So sure when you look at max damage in a level 20 caster, a cantrip can do usually between 32 - 40 damage per round, may sound acceptable, but the problem is, on a missed attack (or a save) you do 0 damage. Minimum damage is 4. So in reality you'll probably average around 16-20 damage in a hit, which fir level 20 characters is pretty weak. A fighter with a +3 weapon and a max on his primary stat is going to do a minimum of 36-38 damage depending on the weapon they use assuming that all 4 attacks hit, and the fighter rolled all 1s. For the most part, cantrips are not strong. They may seem strong when you look at the number of dice, but because of black of modifiers to damage, and multi-attacks, the are actually weak for the most part. I am aware that there are a few exceptions, but exceptions don't make the rule.