They're nothing (repeat: NOTHING) alike.
You are trying to compare druids who were effectively two classes rolled into one (rogue and warrior), and played completely differently, to warriors who will effectively play exactly the same as they do ordinarily with Protection, but with a stance modifier for more damage and not a tanking capability. Druids could also change form in combat with minimal loss to their effectiveness, and still blast out a decent healing cooldown with Tranquility, while gladiators lose pretty much all of the things that make them viable tanks; something the designers have explained to you multiple times.
A Discipline priest takes a talent where they lose Atonement, but get more damage from Penance, Smite and Chastise. The reason it wouldn't be a spec, just as gladiators don't need a spec, is because they wouldn't be able to fulfill another role indefinitely (druids could) and they will still play exactly the same (druids didn't).