Use Sunder Armor as prot tank?

I have been playing for a while, but I guess I can be a noob still sometimes. Also, lately I have been watching a little bit of the OnlyFangs (content) drama and their recent raid to Onyxia and Molten Core.

After the raid it was discovered that some of the (DPS) warriors did not use Sunder Armor much or at all. So I have to ask...

Is it not expected that the main tank use Sunder Armor to both apply the debuff and generate threat? I understand that if more than one warrior in the raid uses Sunder Armor at least once on every boss, the debuff will be applied faster. But if you disregard that, is it not the tanks job to use Sunder Armor?

I cleared MC many times in vanilla, but as a healer, and the gameplay has evolved a lot since then so please excuse my ignorance.

TIA