That's cool. In my experience 3.5 was all about save or die and buff spells.
We had situations where fireball was great. This is why I said: usually. Level times d6 damage in 3.5 was not what it used to be in 2e, as hitpoints were so much higher on both sides of the screen.
Fighters did not fear 5d6 damage, nor did level appropriate challenges.
Maybe with 5e encounter design we had made the same experience as you. But back then we usually did not fight lots of lower level foes.
Different tables, different experiences.
- A 5th level wizard against a party of 3rd level PCs (a hard encounter): A single fireball could easily wipe out 2-3 of them and leave the rest hanging on by a thread.
- A 5th level wizard against a party of 5th level PCs (an on-level encounter): A single fireball could put down the arcane and bring the rest of the party to 1/2 HP or lower.
- A 5th level wizard PC against a horde of 12 orcs: Instant death, encounter over
- A 5th level wizard PC against a pair of ogres: Not optimal, but anywhere between 16 and 35 points of damage for a single action (on average)