Not really. A lot of the “X class can do it too!!” memes and faux-guides rely heavily on you being exceptionally geared, enchanted, consumed up the butt, buffed further, and wbuff’d even further.
Onyxia is one of those raid bosses that almost anyone can “tank” because she melees so hilariously weakly. Like… 10man trash mobs can hit harder than her. Her only real threat is her flame breath, which is still anemic and resistable, and the fear issues. But people use it as a jumping point to “prove” that certain classes/specs can do the same job as everyone else, which is just silly.
MC has been Tanked from start to finish by single digits worth of Shaman, but only at the end of the tier, with the most success coming from the fact that a Shaman can throw on FR gear and be nearly as sturdy as any other Tank while handling an all-fire boss like Ragnaros.
BWL on the other hand really trounces all of that. Bosses hit harder, the mechanics are far more punishing on Tank health/survivability, there are a host of taunt swaps, and the non-Tanks just don’t get gear to keep them progressing while everyone else continues to grow. Shaman in particular just can’t survive the Drakes or Broodlord in BWL and all of the videos and logs of people clearing BWL with a Shaman “Tank” have the Shaman dead on the floor most of the time while Warriors and Druids do the rest of the heavy lifting.
AQ40 is even worse and Shaman have only been able to show off their ability to hold random adds that die quickly (think Sartura and Fankriss) but can’t do O’uro or Twins without insane luck.
Luck is basically the name of the game. If you dodge and parry enough, you can probably live this time but you won’t everytime because you just don’t get that kind of RNG all the time. That’s why you only tend to find highlight reels for these things, not the slogfest that led up to the perfect storm of favorable RNG. Those BWL clears with Shaman “tanks”? Over 4 hours. People clear Naxxramas in half that amount of time without even necessarily pushing super fast or hard.
CL on the pull is great, but it doesn’t hit enough targets to be useful on say something like a skitter pack in Naxxramas, and once its out well… that’s that. You cast while being melee’d and all that luck I talked about above goes out the window because you can’t Dodge or Parry or Block while casting.
Warlocks would be far better at the AoE threat thing, but Hellfire is also self-damaging and those skitter spiders will one-shot the Warlock that pulls all of them.
That’s why Druids and Warriors use AoE Taunts and LIPs, which not only protects us entirely from death, but means the Mages/Warlocks/etc can go absolutely ballistic on DPS, never pull, and not die.
It just… isn’t enough for them.
In TBC Shaman don’t get any better, even if they get loads of Arena gear, because the expectation is that all the Tanks, Druids included, become crit immune while also soaking exceptionally huge damage. Plus, if Shaman want to be able to Parry, they have to give up a huge hunk of Threat on top of it, so they become actively worse.
Warlocks get additional Tank-caster duties like they have now on Twins. A lot of guilds use Warlocks on Leo’s demon form, the caster on Kael, and Illidan during his big-bad-demon mode at the end of the fight. As for more traditional Tanking though… not really. The new talents and gear don’t really beef them up exceptionally well, even if they go Demonology and use a pet to help them out. Warlocks get their own demon form in a later expansion that makes them actually capable Tanks, but it isn’t permanent unfortunately, so its used more like a DPS CD or a PvP survivability/burst combo.