Using a spell slot for damage should generally always be better than the available at will option. That isn't really the case with cantrips and level 1 and level 2 spells. I find that to be a design flaw in 5e. I don't know how to fix it but I think cantrips should never outpace even a level 1 spell IMO.
Thoughts?
Since I had some time this morning, I did a quick review of the cantrips and spells most likely in question. I can see your point and agree for the most part. One change (for me anyway) in going from 1E/2E to 5E, is the idea of spells increased damage coming from being cast using higher level slots instead of naturally scaling with the character level (as the cantrips still do).
But I will play the devil's advocate and argue against your point:
While 1st and 2nd level spells have static damage (unless using the higher slots), they often deal comparable damage to the cantrips from 11th and higher levels, but many times to multiple targets instead of only one, as most cantrips do. At the highest tier, a cantrip will average about 18 points of damage (some more, some less) to a single target, always requiring either an attack roll or failed save or the target suffers no damage at all.
While nearly all 1st level spells will do less than 18 damage, their power comes from the fact that many still do half damage at a minimum, affect multiple targets, have additional effects, deal damage automatically (no attack roll or save allowed), and so on. So, while the 3d6 damage from Burning Hands, for instance, is less than a potentially 4d10 Firebolt, the Burning Hands could hit 3 or more targets, and deals half damage even if they make their save. Oddly enough, 2nd levels spells do even less damage overall than 1st. But, again, the extras of the spells can make up for it. 2nd level also has very nice utility spells which are often more interesting. Finally, even at the third and fourth tiers of play, there are several higher level damage causing spells that will usurp cantrips in power, number of targets, etc. (but that was not your original point, so I digress...).
If the intense damage of cantrips at 17th bothers you, my suggestion is removing that tier's damage boost and offer something else instead (or just remove it and don't worry about it.

) One idea I was playing with at the highest levels of play, is removing the damage boost but allowing casters at that point to employ cantrips as a bonus action.
Either way, I will miss my 15th-level Magic-User casting a swarm of eight Magic Missiles for only one 1st level spell. *sigh* Now, I would have to expend a 6th level slot for the same thing... Um, I don't think I'll do that..