the bolster effect scales. there is a gear grind. if you don't constantly upgrade, while I do, I'm going to absolutely crush you on gear alone. there are no tiers (other than the 3 colors). however, there are levels. and a 25 wearing something for a 15 usually isn't such a good idea.
This. If you keep your gear updated you'll have like 14k hp and higher stats while others have 11-12k and lower stats. It's a big *** difference.
The difference is even larger when you get people who use purp items and augment their gear.