The dev's stated they wanted fighter to be the baseline, or vanilla class, but since the Thief was visibly more powerfull, it spontaneusly became the default baseline class for most people. With Thief as baseline everything less powerfull than the Thief was considered "in need of buffs", and there was a line of thought that "everything should be brought up to Thiefs level". Since we lacked terminology and some of the understanding we have now, just how powerfull the Thef was wasn't obvious. Most of us didn't know that that line of thinking was "make everything ludicrous".
This state of affairs led to 2 things. The direct one was that the devs probably had a good reason to think of the community as a bunch of megalomaniacs - as the community was prone to think of the game around a different power curve than it was supposed to have. The second thing was that whenever the megalomaniacs got their way, something got buffed for the wrong reasons. Imagine trying to bring everything to Rogue or Monk power level?
So fighter became the king of ding. This is fun, ofc, but he really got pushed to being a DING machine, which now makes him more of a spellcaster than a fighter. Classes you had to work to unlock, advanced classes, compared badly to the Thief, so, I, for example, ussually completed most dungeons in a playthrough with either the Thief or the Monk, never feeling any incentive to try figuring other stuff out.
And if dungeon difficulty was measured in "wether Thief can do it", which it silently was, the whole game was being measured with the wrong measuring system. Nerfing the too flexible and too easily available Thief was the start of a long period of bringing stuff in line which results in the current "no worst class" meta. Back in the day, it wasn't possible to do everything with everything.
The reason the thief could use a buff again is because with him out o the way, the "standard item pool" CP bonanza got figured out as excessive (by the community, the dev's made it so on purpose), and a lot of other things which sinergized with him (but was never complained about) got tweaked, so he might not be the "disc one nuke" he was before. Except making him the way he used to be might brink the whole "how does this compare with the thief in terms of flexibility" issue with kingdom development. If the whole CP/potions shtick were a 3rd level or bonus class feature, he'd never be baseline again, so we'd have the class but no learning curve / playthrough issues.
*(Double worth of potions + hoarder CP goodness).
Fun additional thigny:
The "Thief-as-baseline" meta created a really schizophrenic game expirience where the baseline was three steps above the intended baseline but just one from the actual cheeze. But since the baseline was the byword for effortless flexibility, the most cheezy strat, %res stacking, was a rather single minded approach. The average dungeon was too hard for anything below the baseline, and the true power of cheeze was either not public knowlegde or treasured as "viable".
So when the excessive stuff started getting the deserved nerfs there was much wailing and gnashing of teeth, and the vets had to reassure everyone else once the cheeze is brought in line - so would the dungeons. And where we are now, it's probably all good, except the Rogue and the Monk are sort of "what can you do" inherently too good, and the fighter is a fun oddball.
