First, who cares what happens at 20th level? Seriously, most campaigns don't ever get that far, and the issue focuses on where most campaigns will experience the issue. So it's nothing like the 5d8.
About a minute ago I was arguing pretty much the same point you are making (but regarding a different mechanic). I think these are the sorts of "peripheral" aspects of the game where we pick and choose which we care about. In this case, I do care about it. I remember talking to a friend about some 3e houserules and how it would make certain options a bit stronger at lower levels, but a bit weaker at higher levels. He immediately asserted that that was a horrible way of balancing things. Upon reflection I decided that I agree with him, and I still do.
It's true that most campaigns that start at 1st level aren't going all the way to 20th level. But I don't only start campaigns at 1st level. Sometimes I even like an epic campaign.
Second, saying 5d8 with three exclamation marks (and multiple times too) doesn't actually make it more than it is - and what it is, is low damage in this context. 5d8 is about 22.5 damage. It's only 22.5 damage!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
For a 20th level character, this is not particularly meaningful. Due to bounded accuracy, their attack role is still sometimes failing (for zero damage), and the monster they are attacking has a lot more hit points, and often has a lot more means to be outside the range of that spell (but likely still in the range of a crossbow). Meanwhile, they have so many spells, which do so much more damage at those levels, that it's even more silly to be putting three exclamation marks next to 22.5 damage for a regular attack spell requiring an attack roll at 20th level.
Bottom line, your 20th level character won't be common, and even when they do come up, they won't be using this spell much anyway. They're going to wish they had a longer range attack when facing that ancient red dragon.
But that's a playstyle expectations concern, not a given. With the modest number of spell slots given it's quite likely that even a 20th level character is going to use up all of his higher ones in a long days adventuring, and find that 22.5 being his most appealing combat option.
Also, the whole point of this is that those who are most likely to want to nix at-will cantrips are also those who want the style of game where a wizard without his daily spells has the worse attacks in the party. Part of the goal is that the wizard's attacks should have a very small contribution once he's used his spells--more encouragement to manage his resources carefully.
So if he has a built-in at-will bazooka that he rarely uses, he still has it and it effects game immersion experience. And if he has an at-will bazooka in a game that has long adventuring days, he most likely will need to use it.
So we're really talking about much lower levels - levels at which the crossbow does around the same damage. Because ability scores naturally go up but they max out at 20 this way, and because Dex is generally the second best score for a mage, we're talking about +3 to +5 damage for their crossbow (which has a much longer range than the ray of frost). So that crossbow is doing better damage than the spell at low levels, and continues to roughly keep up through 9th level. From 10th to 14th level it starts to do about 4-5 points damage more than the crossbow, which just so happens to be the levels where that 4-5 extra damage becomes less meaningful as hit points continued to go up, your other spells continue to do more damage, and your attack rolls are still failing sometimes due to bounded accuracy. And that's also around where most campaigns seem to end, according to survey data.
Bottom line, for most campaigns, it's a very marginal difference. An awful lot of people will want to choose a different cantrip than an attack cantrip, particularly once they start to crunch the numbers and see how little difference it makes relative to the crossbow, and the added range of the crossbow.
I am glad you like the attack cantrips and think they do AWESOME!!!!!!!!!!!!!! amounts of damage. But my mages will never be taking any of them, unless they find a scroll of them. They're not good spells. I'd much rather have minor illusion, light, read magic, and mage hand.
My mage would likely learn just about every cantrip I can get my hands on. I'd even learn and use attack cantrips if they scaled the way I'd prefer them to (2d8 at 8th level, 3d8 at 14th level).
Remember that attack cantrips come with extra effects; and I'd probably say Constitution is a contender for everyone's second favorite stat.
I think our disagreement here is mostly about whether this peripheral matters. This is one of the issues that feels like it matters to me, and isn't one of those issues for you. No problem, I enjoy most of your posts.
