To be honest I haven't played destiny recently so I can't even remember what those perks do. And believe it or not I was never big on perks. Only ones I cared about were the different scopes on a weapon and maybe a perk for less recoil but that's it. Also unique is a strong word that I believe you are using wrongly. Just because the same exact weapon has slightly different perks doesn't make it unique in my eyes. It's still the same weapon and it will mostly act the same no matter what perks it has.

You come from a PvP background don't You? The sights in this game matter the least for PvE, and the perks in Destiny have a huge difference on weapons. They are very unique and different from each-other, even with a perk like casket mag replacing a perk like extended mag (both Increase mag size, but casket more-so at the cost of stability).

Honestly the sights on a weapon matter greatly no matter what Im doing, the weapon's look also makes a big difference in my performance. And why would 2 perks like extended mags and casket mags need to exist? Why do you need two perks that do the exact same thing (with the slight differences of course). I would rather have 2 different snipers, one with fast RoF with a set perk that's like casket mags and one with a slow RoF but it has a set perk that reduces mag size for more damage. That to me sounds better than 1 gun that can get both of those perks if you farm enough. Weapons that feel unique and have personality, so that every gun is practically a mini exotic, unique and special in their own ways.

Because those 2 perks are incredibly different! A machine gun with casket is way harder to use, but a machine gun with extended doesn't do as much DPS. The difference is massive.