Guardian Angel Overtuned?

This season, adcs are feeling really over powered again - which comes with any number of the usual frustrations. However, I think this item is one of the reasons they're so problematic at the moment. Some of these champions become virtually unkillable in team fights, especially within certain team compositions. Locking them down doesn't really make a sizable difference because the amount of passive healing available to adcs right now is kind of ridiculous. There're abundant sources of healing from runes and items, not to mention whatever healing could be coming in from a support. Furthermore, I don't understand why this item had to be made an AD exclusive item in the first place. It's become a ubiquitous AD pickup, and isn't really a niche pick anymore. It just gives great stats, and comes with great utility. While there are similar items available to the mage class (Banshee's and Zhonya's), I don't think those items quite compare to GA, as they aren't backed up by tremendous amounts of healing, except in the case of particular champs (Akali, Sylas). GA over-highlights the difference between champs that have sustain and champs that don't, and I just wonder why all of that is exclusive, essentially, to the AD class.