How is it a buff? It would only effect PvE games and only against that element type shield. In a nightfall worry that elements burn it would be extra effective as well. In PvP it would only look cool. I think it should be a selectable perk. Similar to the (too early, drawing a blank... Oryx's exotic scout). The last bullet would be elemental and unlimited however it will drain your super. Not sure what the other "sacrificed" perk would be.

It gives it even more reason to be used in both game modes over the other two class weapons.

Not really in PvP. Most of the time it would give no advantage aside from looking pretty.

But my point remains that it would give players just joining reason to level up Gunsnith on warlock more than every other class gun

True. I don't really see the problem with that, personally. If they made a character just for one weapon then that's their choice. There are other great weapons out there which can be used by [u]all[/u] classes, not just Warlocks.

True but no other class specific weapon is nearly as good

Very true. Tlaloc is by far the best. In my opinion it's better than MIDA, even without a charged super.