Well if healers would do, like you say 75% dps of a damage dealer than dps role in PvP is just thrown out. Any "pure dps" will be replaced by healer as only healer spec would be capable to withstand the other healer.
In both way. To heal themself and even to kill the opposing healer. Pure dpser would have no chance whatsoever 'cause if he cannot kill the healer "soon", he will just die "later". So fat chance that Blizz devs will throw balance away in such a way.
On the other hand it would be nice if
Resto Shaman, Resto Druid , Disc Priest would be a viable setup up in Arena
Or just imagine to throw in the above setup also Holy Paladin and Mistweaver Monk and you would have a killer 5v5 combo.
Well you can still dream about that.