Invoker problem is done people think throwing a fireball is a great idea.
You think fireball is never a good idea.
I can still acertain you: in our games fireball (especially if you can exclude teammates) is often enough situationally so good, no other spell could compare.
Remember the 3.5 Warnage which was super powerful?
No.
5E danage spells are so much worse comparatively.
Depends. If you use CR < 1 minions frequently instead of scaling minions up to player level, fireball stays useful.
If you as a DM think that if level 10 heroes never face CR <1 creatures as minion and instead think that the world around them scales with them, so that level 10 heroes face level 8 minions or no minions at all, you are correct.
Comparing 3.x and 5e is moot. In 3.x, Creatures of CR 4 levels lower were no threat at all because of number inflations. Also the game probably because of this featured party vs few high level foes quite often.
Now, in 5e a powerful necromance might still have an army of skeletons and zombies around him. Annoying enough to clear them with a fireball.
Diviners good if you roll well on portent. But its very limited in use 2/long rest in an edition with vad saves anyway. Sorcerer can heighten spell a lot more and is better imho. Every sorcerer has that option.
Yes. And they also take twin and quickened and... Oh no, you just get two option for all the levels you count (< 10).
Diviners portent is reliable. If you roll mediocre rolls, one might decide to use heroic inspiration on that. Or just have a relaxing day and kill the boss later.
Abjurerers best out of those 3.
I like abjurers.
Never seen one though. Sadly our game where I wanted to play one was stopped because of covid19. I have seen all the other three in action, and the transmuter. The transmuter was nice to have. Ironically the most iconic features were good con saves and fireballs (in an official adventure) and slow... and highest strength of the whole party... The other ones all did even better.