Well, not so much. Fireball is good at some kinds of things, but it's not exactly the game-changing powerhouse that some other spells are. For example, as Shadowdweller says, Conjure Animals kind of blow it out of the water in terms of sheer effectiveness (in many but not all situations). Animate Dead has a way better concentration economy than Fireball, even if you're not a necromancer; Polymorph is a tanking spell par excellence; Planar Binding is fantastic at turning gold into combat power; Pass Without Trace is the sneak supreme; etc., etc.
The problem is that you've managed to find the couple other spells with known balance issues and compared it to them. Polymorph is already reported to the dev team as the most broken spell in the game and they've said they were "considering solutions" to it.
Conjure Animals is broken when used in a very specific way that was fairly obviously not intended by the creators but managed to slip through. I can't remember which one, but I think it was Jeremy who said that the intention was for the DM to decide which animals come when you cast it. Which prevents most of its abuse.
Planar Binding requires you to find a powerful creature and trap it in a way that it won't move for an hour. It's not practical in most adventure's that don't have time to sit around for an hour and cast a planar binding. If you even have access to a creature for an hour straight.
Animate Dead lets you animate creatures as skeletons which don't have the best bonus to hit and die pretty easily. Beyond the first couple of levels they either don't really help you in combat or they die every combat and have to be reanimated.
Pass Without Trace is a really good sneaking spell but when you get into combat it doesn't help at all. And most adventures involve a choke point of some sort where enemies WILL see you, even with Pass Without Trace.
Even just considering the pairings you listed above, it's not at all clear that Fireball pushes the Fiendlock over the top, since Evard's Black Tentacles on the Cthulock is arguably better (save for the concentration requirement), especially for a warlock with Repelling Blast. The Fiendlock's temp HP may or may not be better than the Cthulock's telepathy--it varies by table, and at least at my table, ability to communicate telepathically is way more coveted by the players than temp HP since diplomacy with alien creatures comes up pretty frequently. In any case, it isn't Fireball which is creating the tiers, if any. I hate clerics so can't speak for them from play experience, but the Light cleric doesn't really stand out as clearly the best.
In my experience, any situation which is dominated by Fireball is dominated by other spells as well. My Lore Bardlock found Fireball tempting, sure, but ultimately he went with Spike Growth instead, because there just aren't many situations where 8d6 in a 20' radius once is better than 20-40 points of damage to anyone crossing it (at half speed, no less) plus +10 damage per Eldritch Blast (4d4 for 10' knockback) for ten minutes. Fireball is great at killing swarms of drow, orcs or hobgoblins, but Spike Growth is equally good at either warding them off or killing them if they try to close, and they don't even get a saving throw. Other spells like Hypnotic Pattern, Confusion, and Call Lightning can also do the same job as Fireball in any situation I can think of. It's not a must-have, it's just nice to have.
Here's the average situation adventurer's find themselves in:
"You walk up to the tower and open the door. Beyond is a 30x30 room with 5 Cultists. The closest one is 10 feet from the door when you open it."
We've ran into this situation in about 60-70% of all our encounters. Our party that had 4 different people who knew fireball solved these EASILY with:
"I cast fireball" "Alright, 2 out of the 5 of them die."
"I cast fireball, as well" "Alright, the other 3 die."
In an average combat we took literally 0 damage because no matter how many enemies there were in a room they were dead before they took actions.
We got so used to it that during the 1 time in 20 when we had an encounter that made fireball useless the party was at a completely loss as to what to do. One of our players used to get super angry whenever the DM would tell us to keep people alive or put random captives in the room with the enemies since it ruled out his fireball everything all the time strategy. Very quickly he decided that his character didn't care about keeping anyone alive, even prisoners and started fireballing those rooms as well.
I can tell you that the one time some decided to "get smart" and cast spike growth, the enemies all pulled out ranged weapons and focused on him until he failed a concentration check. He successfully did 0 damage and managed to get himself attacked a LOT. As for the knocking people back through it and forcing them to take damage, you should expect table variation on the ruling for that one. It says when the enemy "moves through" the area, not when they are knocked backward through it. Plus, many DMs who ran 4e know that forcing someone to move through an area and take damage became such a broken thing that almost every spell that allowed you to do it was errata'd to be once per round. Even from a role playing point of view, I think the point is that you step on all the spikes along the way and being knocked back might not involve you feet touching the ground. I know I ruled that people flying through the area weren't affected at my table.
Although Hypnotic Pattern and Confusion are both good spells, they don't do the same job as fireball. They slow down a couple of enemies but they don't kill them. You still need to use other spells or other actions to actually defeat them. Trust me, I kept TRYING to use Confusion instead of fireball as my Bard. My entire group would make fun of me. They'd be all "Well, you managed to affect 2 enemies with your confusion, it has absolutely no effect on the ones that made their saves, they get a save every round and if they roll 'attack nearest creature' or 'act normally' your spell generally doesn't do anything that round. You could have fireballed and just killed them all instead. I can not only fireball but do so in the middle of our party and ignore all our party members using my evocation ability." So I eventually used my Bard ability to pick up Fireball and then combats went even faster than before with a lot less rolling of constant saves to see if people saved that round or what actions they'd take.
Its damage is just too high. If it was lower, I'd agree that it's ONLY useful against a bunch of low level creatures. But if your choice is between a 5d4+5 Magic Missile, a 5d6 Burning Hands, a 8d6 Scorching Ray and a 8d6 Fireball, you pick the Fireball, even if there's only one monster.
