There were only DPS in 4.0 and people were "Huh???" about this. With same case in 5.0 the reaction could be even worse (it is quite bad with no new healer already). And well, Yoshida-P explained well, why they decided to add new Tank.
Somehow, I personally waited for GUN for 5 years and always though about it as about tank so I'm on happy side of boat, though I do understand why some people were disappointed - not all players like to play tanks overall. It was quite the same with Dark Knight.