In 5E, I'm OK with the way they are. Not entirely satisfied, but OK. I'd prefer that the cantrips had a burnout process as the default, with an optional rule to ignore it, getting back to the current 5E rules in the process. I don't mind that cantrips get used a lot. I do mind that the only cost is the opportunity cost of not casting another spell. Of if you hate burnout, then give cantrips a slot count but make it generous--maybe equal to the casting stat. A wizard with 16 cantrip slots is going to still use them a lot but there will at least be a little hesitation at times in favor of letting the martial characters handle things.
From a game design perspective, I dislike the way that D&D cantrips (over multiple editions) are shoehorned into the front of the spell level system as a special thing. Sure, in AD&D, keeping compatibility, there is a good reason for it. By the time the WotC editions came along, if we are going to have some weaker spells at the front of the progression, then monkey with the spell level chart to smooth it out. (There's some work to be done at higher level spells, too, but that's neither here nor there for cantrip discussion.) There's a lot of sharp edges in the design in the pursuit of putting more and more elements into the game while keeping burning hands and magic missile and sleep as 1st level spells.