If I remember correctly at the end of WoD conquest gear would jump 40 item levels in power when you were doing Arenas or Battlegrounds. In PvP you probably felt felt good having whatever the desired stat spread was but outside of that you were 40 item levels weaker. 25% crit was only 18%. Mastery, Versatility, Main stat was all a set % lower. Not only was damage lower but everything else was lower too.
It meant that you spent all this time gearing up, capping conquest, pushing rating, and buying gear only to have someone kick you from a raid you might have wanted to pug, or get declined from challenge mode runs because BiS at your ilvl isn’t what BiS at dungeon ilvl was. You put all this time into the game but you were treated like a lesser player and basically performed like one out of no fault of yours anywhere that wasn’t a battleground or arena.
Item budget at these item levels was way off iirc, individual item strength when you compared the honor version, last seasons item, and the next seasons item was way off and then player strength was also scaling through the roof with the secondary attunement passives, insane ilvl trinket procs, disproportionate gear upgrades etc.
There were a lot of problems that I can think back too and remember in hindsight even though I personally enjoyed the system. I don’t view it as failure but I acknowledge improvements could have been made.