What could DRK have learned from FFXI?

[Reynhart]

SE choose the tank since the HEAVY armor theme suit more into tank into FF14 structure

Nowhere the OP suggested that DRK shouldn't be a tank, only that FFXI DRK iteration had some interesting skills/spell that could be added to XIV's DRK to make it a more unique tank.

(dont say Dragoon can use heavy armor, coz his own "iconic" JUMP was based on elude enemy attacks and deal double damage in old FF, that suit more as a damage class then tank in a MMO structure like ff14

Hmmm, you can't really use "Jump" as a reason to why DRG shouldn't be made a tank when sacrificing HP to do damage is a concept that you would definitely don't want to see on a tank (In its basic iteration, at least)