Originally Posted by
Hitei
"Armor set number" Comparisons are a pain in the ass because of how armor gets thrown around everywhere, recolored, reused in various places, and the existence of random pieces that aren't parts of sets, but at a rough glance looking at their respective launches (ignoring Crafting which I assume is the same):
Legion
Tier 19: 12 (EN/NH)
PvP: 12
Questing: 8 (there's a lower level set and an upper level set, the upper level is also used for dungeons and WQs)
Demon Hunters: 2 (a green initial set and blue "upgrade" set)
BfA
Uldir+Azshara: 8 (4 for each raid of the first tier)
Questing: 8 (4 on KT, 4 on Zand)
Dungeon: 8 (4 on KT, 4 on Zand)
Warfronts: 8 (4 Alliance, 4 Horde)
Allied Races: 4 (Mag'har, Dark Iron, Zandalari, Kul Tirans)
So basically exactly what they said, they stepped away from Tier sets and wanted to focus more on sets that match where the armor is coming from. The upper and lower questing sets became KT and Zandalari sets, and PvP/Raid tier lost 8 sets total, that became 8 dungeon sets based on their respective locales--with the rest of those becoming the raid sets and warfront sets.