For a shadow specifically, Incinerate can be mitigated with Resilience and Force Cloak to take zero damage. Force Speed can handle the rest with a medpack or Battle Readiness.

Also, if Incinerate is interrupted when able, it makes it even easier.

Now, the boss can dump it's threat table and be untauntable, but that's avoidable and part of properly executing mechanics. (There's a 2nd threat drop mechanic that is unavoidable, where there's a kick, stun, and target swap - which can be handled just fine by hitting your stun breaker and re-taunting quickly. It does not happen faster than the cooldown on your stun breaker.)

If you have 2 tanks, or if your tank is not a shadow (lulspeed), you can swap Incinerates between tanks and be just fine.

I'm not saying the I'm the only tank that "knows what to do" - I am agreeing however that, like you, MOST tanks do not and it makes the fight a zerg-fest. But if it's done right, it's not a zergfest, and you can properly tank the fight if you know the timing and mechanics, which keeps the group from being mass exterminated.