True, but at high level, your save DC becomes relatively much better (monster saves stay relatively low). So while the DPR (damage per round) of a 1d10 low-level cantrip might not be much more than half of the average of 5, the DPR of a 4d10 high-level cantrip is easily 80% of the average of 22.
And so while the damage dice is "only" quadrupled, the actual DPR might have increased by a factor of seven.
(Example simplified for clarity)
Regardless, a cantrip failed save means no effect or damage.
And 22(4d10) damage at 17th level is no different than someone firing a bow, or swinging a sword at the same level, and stacked next to a melee class that spell attack cantrip takes one action of the spellcasters action economy, whereas, a weapon attack benefits from extra attack.
This is pretty much incorrect. Many cantrips require an attack roll, not a save. Since casters are about as likely to hit as warriors, this makes casters at higher level pretty good damage dealers with cantrips alone.
This is pretty much incorrect, only 6 cantrips require an attack roll (Chill Touch, Eldritch Blast, Firebolt, Produce Flame, Shocking Grasp, Thorn Whip). From SCAG, Booming Blade and Green Flame Blade have a situational side effect which does not require a saving throw.
Magic Stone, Primal Savagery, and Shillelagh are exception to the above, but they do not scale. Primal Savagery, and Shillelagh being Druid only as well.
of the 6 scaling spell attack cantrips:
- Bard gets 0 but does get access to Magic Stone
- Cleric gets 0
- Druid gets access to 2 (Produce Flame, Thorn whip), but also gets access to the 3 non-scaling weapon attack cantrips
- Sorceror gets access to 3* ( Chill Touch, Firebolt, Shocking Grasp)
- Warlock gets access to 2* ( Chill Touch , Eldritch Blast)
- Wizard gets Access to 3* ( Chill Touch, Fire Bolt, Shocking Grasp)
*Also gets access to the 2 situational cantrips from SCAG (Booming Blade, Green-Flame Blade)
So we are really looking at 3 classes here, Sorceror, Wizard, and Warlock, who have access to a 1d10 scaling spell attack cantrips.
The cantrips being Firebolt for the Sorceror and Wizard, and Eldritch Blast for the Warlock.
Again, action economy, the arcane caster firing that one shot, versus the melee classes Extra Attack. Quickened spell is an option, a few bonus action casting cost spell slots might be used, but these are finite resources where the Extra Attack always happens. Warlock invocation enhancement, Agonizing Blast, ups the damage a bit, but the former limits still apply.
Also, they still have to hit with the attack roll. Higher level mobs have better defenses ( AC, resistances, immunity).
I think the real argument for OP comes with high level stats on chargen, or when feats, and multi classing are allowed ( or even perhaps allowing arcane spellcasters to wear armor ...looking at you Mountain Dwarf Wizard!), if you have issues with the at will attack of your casters, then do not allow feats and MC. Personally, I've never seen this be an issue. What's good for the goose is good for the gander, the adversaries are using the same cantrips...