Well, the average turtle PLD was always obsolete and incapable of tanking at all. That's a given. DDs may hit hate cap in 15-30 seconds these days, but that does not mean they were unable to easily hit it in 60-90 seconds pre-Abyssea.

You're absolutely right when you say all jobs are/were capable of crossing the line. Heck, in some cases (SAM, MNK, DRK, sometimes NIN), "DD" jobs were better tanks than PLDs were long before Abyssea came out. Really, the only reason a lot of good players were unable to tank regularly on those jobs were misconceptions by their group, especially bad/mediocre White Mages who had a tendency to only focus on curing "Tank" jobs while everyone else could just die and it would be "their own fault" (this makes me rage so hard).

When it really comes down to it, Paladin has never really taken much less damage than any other job with equivalent defensive gear. Most every melee job can cap PDT and MDT in sets if they so choose, it's simply a matter of getting a competent player who actually has those sets. Shield has always been a bit of a crapshoot, and other jobs can most definitely match Pld's Enmity gain and damage reduction in other ways (Seigan, Stuns, Counters, etc).

I suppose what I'm saying is, in an environment with higher end players who were able to deal lots of damage on their DDs and had proper gear sets, Paladin has been obsolete for a very very long time. It just seems a bit more widespread now because, in Abyssea, even full Aurore trash can deal respectable damage with Atmas and Cruor buffs while rocking 3,500 HP, while even full teal Whms have infinite MP.

The problem has become more visible to social/casual players, but most higher-end endgamers have been seeing this for years now.