Hussar
Legend
Technically, 4e & 5e both use the term 'tier to refer to a range of levels. But the class tier concept was a 3.5 fan ranking of classes, primarily by versatility. Prepped casters able to change their focus on a daily basis were Tier 1, spontaneous casters, with a fixed list if known spells but flexibility in which ones to cast repeatedly were a hotly contested second. Fighters, able to customize their 'build' with a bonus feat every-other level, were Tier 5. 4e put most classes on AEDU, giving them rough parity in versatility, and, until Essentials all classes were compressed into what, in 3.5, would have been a single Tier.
5e returned to more traditional class designs, though with some interesting differences, significantly, all casting is now spontaneous, so prepped casters are more versatile than ever, and 'Tier 2' casters further behind them...
...Fighter's non-casting sub-classes, OTOH, well, they do produce some very competitive DPR, as you pointed out. Which -being good at one thing- puts them solidly in Tier 4.
FWIW.
Nothing about Tier rankings stops an enthusiastic player from having fun with the concept he genuinely wants to RP, and sufficient system mastery can make use if a lower tier class to create quite potent builds. I played a fighter-based, non-casting build for years under 3.x, myself, it remains a favorite character.
But, you're ignoring a big elephant in the room (heh) in that analysis [MENTION=996]Tony Vargas[/MENTION]. The spell lists in 5e are VERY truncated. To the point of being absolutely emaciated compared to 3e. Even core 3e had FAR more spells available, particularly for clerics and druids, than 5e does.
I mean, in 3.5, a cleric, if nothing else, had Summon Monster at 1st level (plus the entire suite of summon monster spells). And, going up the levels, clerics got AOE damaging spells. like, say, Searing Light at 3rd. A 5e cleric has pretty much no AOE direct damage spells until 5th level with Flame Strike (to be fair, they might get some from their domain, but, that's not guaranteed). They do get some damage spells, but, not too bloody many. The cleric list is about 1/2 the options that a 3e cleric got. Same for all the caster classes.
And that's not including supplements. Now you've literally got thousands of spells for any of the caster classes.
If you took 3.5e clerics and wizards and restricted them to 5e spell lists, suddenly those 3.5e tiers would be a LOT closer together.