If a guardian can take an axe to the face from Alakhul and a arc mortar blast from the second shield brother, then why cant they take more than one bullet to the the skull from a sniper?

Supers are not hard to shutdown without sniping.

Its about time Snipers got nerfed, with all that aim assist, Im suprised it took so long

Unfortunately for you, you don't appreciate the creativity of each guardians super ability. For example, Bungie could have been way more creative and made weapon type interactions such as arch is weak to arch, void is weak against void, and solar is weak against solar. Continuing with the example a Warlock in their sun singer would soften any incoming bullets that are not solar based damage due to the immense amount of sunlight being radiated from their bodies (intrinsic perk is increased armor against all types except solar). Now arguing for realism in a fantasy space game is also a mistake. The idea that a sniper should always "one shot head shot" is obviously a mistake as explained by the aforementioned example. The flip side of the realism argument is that shotguns should be able to kill players from 100 feet away instead of having to shoot pixy dust on them at punching range. Supers are meant to be challenging. A single sniper shot should not equate a super that takes time and effort to build up when you can simple find or wait for an ammo create to have multiple super ending shots. Welcome to the old days when a blade dancer would pop their super and you run like hell. Supers should be scary, especially the roaming ones.