Should be. Apparently everyone can equip the shields as well, meaning you can finally get rid of the empty hand slot for the mages. The characters who can dualwield can also apparently equip 2 of them, giving them even more of a stat bonus than others can get.
Damned imbeciles. Why do you wish to fight? -Bahamut, FF8
Sounds like it's still great armor, but not as great as the Adamant Armor could be in previous games. It's hard to keep track of which versions of the game had which versions of the armor, since it seems to change for each version, but various versions of the Adamant Armor have had 100 Defense, 100 Magic Defense, resistance to all eight elements, immunity to almost all status effects, +15 to all stats, and 99% evasion. Now, no single version of the game has had an armor with all of those at once (most recent DS version had all of those except I think 30% evasion boost), so it's never been as completely broken as that list sounds, but it's still been pretty ludicrous in every version of the game. Well, it wasn't quite as good in the GBA version, leading other options to arguably be better for at least some characters, but it was still great armor.
The Adamant armor pieces in this game are less broken, since the bonuses are split up between multiple equipment slots. I haven't seen the full stat listing, but it sounded like equipping a full Adamant set in TAY would be about equivalent to equipping the Adamant Armor in FF4. That doesn't leave the other slots open for other options though, like all the new special accessories. Fair tradeoff for Adamantite being so much easier to acquire than Pink Tails in FF4 IMO.