PLD has always been a great OT since 2.0. PLD OT became that much better with 3.0 additions. PLD was crap in 1.x.

WAR has always been a great MT since 1.0. WAR in 2.0 lacked a bit, but as a matter of fact, only things WAR couldn't solo MT in 2.0 were T5 and double Dreads in T4. WAR MT became a power house in 2.1 and beyond.

Nothing changed for these tanks in 3.0. These two just got better at what they do in both roles, MT and OT.

DRK is a great MT in magical fights. DRK has the same basic defensive CD structure as PLD. DRK OT lacks utility but brings good DPS.

As I said, any combo of tanks works perfectly as long as you know who should do what.