Why be anything else when you can be a :
Melee ranger
Tank ranger
Dps ranger
Heal ranger
Rangers might have more possibilities in other games but here, you are overpowering one class when other classes like mage are being forced into support, why should rangers have so many options yet mages have support or not even bother
Each class is special for a reason and this would take away the whole idea of keen eyed strong marksmen this game has built up for 7 years
Im no ranger so i cant comment on the validity of each builds but rangers have always been a jack of all trades class with a emphasis on dps. I believe when i started playing back in 2011 thats even what it said in the class descriptions. Rangers can have a decent heal, exceptional dps output, can have a melee based build etc. So why not make them a be able to tank in a pinch? This idea also makes a worthless skill a little more useful as well. Big +1 from me, would love to see this implemented into the game.
Edit: Rangers arent the best at everything in every area (besides bosses that are literally meant for them to excel at) because they can fufill so many different roles. If you want to specialize in something like tanking be a warrior, but if you want to be the most flexible of all classes pick ranger.