Currently, Firebolt out does Magic Missile pretty easily in terms of what I would choose for a quick burst of firepower. Now, if I want to hit 3 enemies in one turn but sacrifice some damage to do it, I might choose magic missiles, but as it stands my wizard has been running around out of spell slots for 3 or 4 combat encounters now and I really don't feel any need to long rest to refresh them because him and my Eldritch Knight using firebolt on each of their turns is so absurdly OP that taking the long rest doesn't even seem worth it. I also just remember, in the middle of typing this, that my wizard has arcane recovery. Haven't used that once so far because cantrips are just so useful that his spell slots aren't really needed. The only time I've really gone out with spells so far is when the enemies end up getting to close to my wizard, which doesn't happen very often because of the nice little trails of fire and ice his cantrips leave all over the place to slow their progress.
But while we're comparing using cantrips to using say, 1st level spells, Firebolt out damages Magic Missiles. Max damage I can roll on Magic Missiles is 15 (1d4+1 per missile) while max damage I can stack up from a single firebolt is 18 (22 counting the burn at the start of the enemies second turn). That level of firepower already out performs several of the 1st level spells in terms of damage potential, and it also creates a fire surface that can burn other enemies that walk into it. Ray of Frost might not out damage 1st level spells, but considering how often it knocks enemies prone it doesn't really need to because it's basically a "skip an enemies turn for free" cantrip. And so far I haven't come across any spells as powerful as tossing down an Acid Splash to deal damage and reduce AC in an AoE, which just further increases my odds of hitting attacks afterwards.
Firebolt burst is 7(3.5 + 2.5) if you hit, if you don't, it's just 2.5 and then another 2.5 afterwards assuming the creature is alive. So that leaves you with Magic missile 10.5, magic missile can also be increased by one per level and there's also an item that adds another 2.5 per MM that's in Act 1. I would define burst damage as immediate damage. You can also factor in crits, but if you do go ahead and factor in an average hit rate of 65%. So, easily isn't the correct answer here, if you want to compare cantrips we can also compare Eldritch Blast. One way or another, firebolt while respectable isn't what anyone would define as quick burst of firepower unless you have no other option/resource.
Long rest is also free currently, you're just being fucking lazy which is fine because I am also lazy, but on the flip side I cast MM because I want combat the end sooner rather than later and I also happen to that aforementioned item (also, I don't need to hit).
So I don't think burst damage is where firebolt is at nor is it going to be damage efficiency, but where firebolt does shine if we're talking about pure damage is when you start limiting the spells per day / rests allowed. I mean, honestly, it's better than attacking with a bow.
But let's talk about your comparison to other level one spells and other cantrips, like say frost bolt versus grease; grease can again be bolstered, but keeping it at level one it has a larger area by far than frost bolt. Also, it has better synergy with firebolt but that requires two actions to be used so that's mainly there for food for thought. Would I say frost bolt is better than grease? In most conditions where you're being ambushed or having to fight... say a Boal spawn I would say grease is the better pick. But again, if I don't have spell slots then sure frost bolt is better than firing my bow.
And sure, Acid Splash is great, but again it's not going to be your first, second or even third spell under many conditions if you're playing with resources and playing optimally.
Are cantrips strong? Certainly, but they aren't the end-all-be-all that you're painting them out to be. Go ahead and fight the minos with just cantrips alone and nothing else or fight the phase spider queen with nothing but cantrips, see how many time syou win with four wizards, figure out how long it took and how many reloads it took, then take a normal party and play optimally and see the difference.
