Umm no,
Considering my shell usually use's two PLD tanks at events, PLD is definitely not dead. And no other jobs can't tank nearly as well. What your talking about is Abyssea, and inside Abyssea WHM's get so much MP / Refresh Atma that they can just Cure V - > Cure V -> Cure V over and over again on a single melee without any issues. A melee with DD flavored atma and a tricked out WHM can survive indefinitely against most NMs. In this situation a PLD offers nothing over a WAR for red procs, and you'll already have a WHM for yellow procs, so no PLD means more loot for everyone else.
Once you step outside abyssea all that changes, even now a MNK trying to "CS tank" will get his face stomped on anything voidwatch or even old school HNM (Gates of Hades and Fulmination can still wipe you at 90). PW / AV will still destroy you if you don't carefully plan, and yes bring along PLD tanks.
PLD's are the best tanks in the game, their mandatory for big alliance battles. Their just like DRK, DRG, SAM, ect.. in that their simply not needed in "low man" content of a party or less. Doesn't stop you from going, heck their still nice to have on those low-man battles.