Low level: OK, so I pull out my crossbow and deal d8+2 rather than d10 (most of my nonwarlock spellcasters do not take a combat cantrip until 4th level).
You are assuming that the wizard would be as good a shot with a crossbow as with a spell, which is not an assumption I would make. The firebolt is better.
It really depends on what your issue is. If it's the fact that combat cantrips become better than low level combat spells, then remove the scaling bonus (or half it). If it's spamming in general, then you want to limit their use, and I like the idea of making it a short rest recovery. Cantrip uses equal to proficiency + spellcasting ability would give a tight, but workable amount, forcing spellcasters to mostly use weapons in combat. A more lenient option would be to limit the use of each cantrip to that amount, but that would create a lot more bookkeeping.
I showed you my assumption - +2 to dex. That is common amongst wizards. Not all have it, buyt most wizards, sorcerers, and warlocks (outside Hexblades) tend to have at least a 14 dexterity. You're 1 less likely to hit (5% less likely), but your average damage goes from 5.5 to 6.5 (over an 18% increase in damage). Even with a 12 dexterity, you have the same average damage and only miss one extra time out of every 10 strikes. That is not insignificant, but it is not game changing either.You are assuming that the wizard would be as good a shot with a crossbow as with a spell, which is not an assumption I would make. The firebolt is better.
This.At low levels, it doesn't matter that much.
At mid to higher levels, once multiple attacks come into play, a wizard with only a crossbow and no spell slots might as well be sent into the kitchen to make the rest of the table nachos. Because they certainly aren't adding anything useful to the fight.