In VoG hard you can't revive teammates so your invisibility argument is useless. Invisibility doesn't get you past anything except for the Gorgon's maze which is incredibly easy even without invisibility. Bladedancing will get you killed. Golden gun only helps for taking down praetorians or supplicants effectively but those are easy enough to handle. Golden gun can take down oracles but oracles are really easy to destroy with raid weapons. Titans have bubble which can lock down a vex timegate, offer protection, and either increase shields or damage. Sunsingers are self explanatory and they have fusion grenades which do the same amount of damage as a rocket. Titans and warlocks have more useful supers therefore they are more preferred over a hunter.

Titans have either a debuffing grenade which is incredibly useful in hard mode, or a huge bubble to protect your team, which is again incredibly useful. Warlocks could cheese Atheon, thus everyone wanted them. Now though they just have the ability to revive themselves, meaning if you all wipe you get a second chance without going back to checkpoint. Hunters have nothing beneficial to teamplay. The job a hunter does any other class is capable of at the same time as having the aforementioned abilities. I'm a Hunter by the way.

As a Warlock, it's probably because us and Titans can push Atheon off at the end. Warlocks also have self-res and Titans have the shield. Tends to be more useful support-wise than the pure offensive capabilities of the Hunters. Although in terms of the Atheon fight, I find Hunters very useful with their golden gun in taking out the enemies in the portals.