Bacon Bits
Legend
Do you want them to be weaker?
I think most people would interpret it that way, but no. I really mean a total overhaul.
My biggest complaint is that I want fewer spells that solve adventures. For example, if the PCs find out they need to talk to a Sage that died hundreds of years ago, I want them to solve that problem by going on adventures. I want them to travel to the afterlife and find her, not just cast True Resurrection. If they want to travel to Arcadia to find her, I want them to find a spelljammer to sail across the Astra Sea, or locate a portal to Sigil, not just cast Plane Shift or Gate or Astral Projection. I think Teleport is an awful spell that belongs in this category, too, simply because it does so much and then tries to "balance" it by sometimes damaging the party... in a game where you can so easily rest.
The real problem with the above spells is that they don't actually do anything in your average home game. All they do is force the DM to move where the adventure is so that the spells don't progress the campaign. You still have to have stuff for the players to do, after all. You can't actually just let Gandalf and Frodo Teleport to Mt. Doom, chuck the One Ring into the fire, and be home in time for second breakfast. That's not how the game works. Instead of making the adventure about the ordeal of travelling to the afterlife to talk to the ancient Sage, you just move all those encounters to stuff that happens on Arcadia, or as quests for the Sage. So the spells don't actually solve problems, they just move where the adventures have to be in the storyline. That means at a design level, all these spells don't actually do anything. So what are they doing in the game at all from that design-level perspective? We've just determined that they're non-abilities. It's the same problem as the 2014 Ranger's Natural Explorer, which stops making sense when the game includes long rests that eliminate day-over-day attrition.
Worse, though, is that these adventure-solving spells kind of break publishing high-level adventure design. Do you write an adventure that requires those spells? An adventure that says, "For characters at levels 14-20 as long as you have one Wizard or Cleric"? Or one that bans them or ignores that they exist? Teleport just happens to do nothing anywhere the adventure is taking place? Plane Shift isn't useful because finding a planar key is always harder than traveling to the plane by an established portal? How do you write an adventure that supports both one group of players that don't have full spellcasters, and this other group that has a Wizard, a Warlock, a Bard, and a Cleric?
So I think there's a whole class of high-level spells whose primary effect on the game is limiting the DM's options for adventures and making publishing high-level adventures a total nightmare.
Second, there are a lot spells that I think should be removed as spells and added as magic items or otherwise limited-use options or curses. Some are just poorly written, resulting in them being much more powerful than they have any right to be, but all of them are basically magic items that all Wizards get. Simulacrum, Forcecage, Magnificent Mansion, Clone, Demiplane, Feeblemind, Imprisonment, etc. I don't think they should be on-tap abilities or class-restricted abilities, but instead should be things you find or quest to accomplish. I don't think them being in the game as they are is an improvement to the game at all. Nearly all of them used to be spells that were primarily intended for NPC spellcasters or had so many limitations that the PCs wouldn't want to use them very often. Well, they've slowly removed all those limits and hindrances. Now they're mostly just silly for existing.
Third, nearly all the direct damage spells at higher levels deal the same damage as an upcast Fireball with a novel area of effect. Sometimes they aren't even that good. That's really dumb, and I don't think the problem is with Fireball. I don't even think Fireball dealing 8d6 has proven that it's actually above par for what a 3rd-level spell should be, and that just makes me think high-level spells should have a different par for damage than they do. High CR creatures just have so many hit points now. High-level damage spells should do more than the same "indiscriminately damage an area for (spell level + 5)d6 damage of a fixed type". Why aren't they more flexible like Chromatic Orb? Why aren't they more discrete like Chain Lightning? Why aren't there more like Sunbeam or Vampiric Touch that are transformative? Why are all the blaster spells just more Fireballs when Fireball has a built-in upcast?
That's not even getting into how messed up high level divine spells are. Why are there are so few spells at that level for divine casters? There are nine Clerical spells at 7th level. There are four Clerical spells at 8th level, and four at 9th level. That's not just Basic, either. That's with all the splat they've printed. The divine damage nerf doesn't really make sense at high level, either. It's fine for clerical and druidic bread-and-butter spells to be sub-par or limited for damage, but high-level spells? Divine spells at high levels should be few in number and less flexible than arcane options, but it doesn't make sense that they should still have a damage nerf.