When followers hit level 100 they unlock item lvls much like your hero. If you don’t have much time to play at the start, they can quickly outlevel you in both normal levels and ilvls until you have some time to catch up!
heavily reinforced armor enhancement power overrun weapon

And the Hearthstone upgrade that isn’t really an upgrade but a replacement (it replaces a trait)

hearthstone master wow

Later on with a war mill in operation, you can churn garrison resources into new sets. You can also get 630, 615 armor sets or weapon sets from the 615 quests or war mills.

war ravaged from war mill blackrock weaponry 630 wep