Are you sure about prot paladins on illidan not being able to tank the shear? I remember it being a problem for druids but I feel like decked out pallies it was ok. That being said if you've got the appropriate gear all the tanks can do well in like 95% of content and they shine in certain niches.
I wasn't in a cutting edge style guild back then we did clear BT, but not sunwell before prepatch, but I don't remember us thinking of ferals are super well scaling tanks. Just like you said warriors were best overall. Paladins were the aoe gods, and ferals were the best offtank/offthreat god and deliver by far the best dps out of the tanks. Ferals despite never being uncrushable seemed to have their own strenght in being able to generate a lot of threat without a lot of incoming damage. Thats why a lot of pallies/warriors had to result to stuff like /sit macros like other posters have referenced.
Like I've been telling my retail guild the best setup imo is to have one of each, which is good design imo. Warrior as main main tank, and the feral or pally being the secondary tank depending on the situation (The druid might be doing kitty more than they like if they are big about tanking). And yes it is a little oof that warrior is still the best, but even warriors had their weaknesses. I remember in bear runs they were not the best tank to bring. The ideal tank duo was a pally/feral.
And to the person that referenced warlocks hating their life... so true lol. I remember whenever me and the lock boys (I switched off lock mid t6) got the paladin blessing AND the shaman totem it was . It seemed like threat was kind of the limiting factor for warlock dps in too many situations back then especially if you outgeared the content.