I remeber the times when I was aked how much HP u have, how much block u have, no1 cared about how much dps I can deal, all they cared was to be able to stand high dmg. Now every one they asking me, how much dps u can deal.
Therefore I don't think that the role really changed by itself, what changed is the knowledge people have about the game nowadays.
Defensive sets are completely 'annihilated' in groups who really want to succeed demanding instances. HP cleric or chanter? Exchanged for Mboost or Atk/Crit sets. Defensive Templar? Became useless with the stigma update (4.8) (stigmawise) and defensive sets never had a point, but were sort of an artificial demand the players made up.
Tanks and healers have different roles to perform if they want to be really acknowledged. At least so far. Who knows whether they want to change this a lot in the future. In fact there are quite a few weak classes though which are indeed more useless than a templar (e.g. ranger, aethertech) or they become useless if there's too many of them (regarding their dot skills). Therefore I don't think it's justified to mourn the templar if there're worse classes.
Oh an both Narakkalli HM alliances do have a templar even if e.g. gladiators could be more useful - but templars can take Cold Strike by themselves quite often and therefore take pressure from the clerics. There are other solutions, but a templar is one of the possibilities given. And there's no class you can't survive without everything except for cleric.