I guess it really comes down to this- how many short rests per game day is required to balance 6-8 encounters, if that's even an ideal we're supposed to strive for?*
*There's been a lot of discussion on this point, I don't want to crack open that can of great wyrms specifically.
About 18 months back, give or take, someone presented math saying 2 short rests per day was expected, so I put house rules into place disallowing more than 2 without a "plot coupon". Because having some classes on a short rest clock and others on a long rest clock was driving me batty. I was hearing that if I gave few too short rests, some classes just don't function, and if I gave too many, I'd be shafting the long rest casters.
So how about before we go on about how many people use or don't use house rules like this, we establish some ground rules for discussion, otherwise we're going to see another 17 pages of "fireball is weak (monsters too tough, ideal AoE patterns are hard" vs. "nuh-uh, fireball is too strong (breaks DMG guidelines/out-performs all other similar spells" as everyone cites their own anecdotal evidence?
By what metrics should we be judging fireball? Me personally, I feel the ideal time to cast it in game is at least 3 targets, no allies, no resistance/immunity. I might be able to burn a 4th level spell slot on it, but my 5th and up spell slots are way too useful to use on a few d6 of damage. I know that when the stars do align, I know I'm not going to kill anything I'm using it on (and, barring some weird edge cases like swarms or things with damage auras, anything I could kill with fireball has no chance of hurting me and I can just cantrip it to death unless i'm somehow pressured for time) because it can already fail to kill a CR 1, and I've seen CR 3's who could tank maximum damage from an 8d6 fireball no problem (Yuan-Ti Priest is just one example, 66 hp and advantage on the save).
OTOH, while nerfing monsters offense into the ground is great and all, fights don't usually stop until hp are depleted, and a good damage spell synergizes with what the non-casters are doing, which is almost overwhelmingly some flavor of physical damage. And there are caveats- Evocation Wizard being a huge one- nothing like being able to drop fireball right on top of the melee.
But what is a good damage spell anyways? How often does it need to be cast? Should it have a side of control? Be hard to resist? Be friendly to allies? Have an easily usable area? What type of damage should it deal? How much up front damage is worth casting? How many rounds of, say, Spirit Guardians, would you need to equal one casting of fireball?**
**I think it's 2. If I'm wrong about that, feel free to jump in and say as much.
Anyways, those are some of the questions I'd like to see addressed. I now return you to the ̶u̶n̶e̶n̶d̶i̶n̶g̶ ̶a̶r̶g̶u̶m̶e̶n̶t̶ spirited debate in progress.