To be fair, PvP servers had their own glaring issues. If you were on a PvP server that was unbalanced, i.e Bleeding Hollow as Alliance or Sargeras as Horde, you were pretty screwed. Not to mention, you could technically “turn off” PvP server similar to War Mode if you were invited by someone on a PvE server and sharded over. You’d be placed under their server rules and same vice versa.
I believe those were some of the main factors of them getting rid of PvP servers in favor of War Mode: unbalanced servers and cross server features.
To elaborate more on the cross server feature thing, if a player on a normal realm joined someone’s LFG listing and that player they joined was on a PvP server, they’d get flagged for PvP too, despite that person picking to play on a PvE realm.
I think people also forget about the territories too. PvP servers weren’t “you’re flagged 100% of the time.” If you were Horde in Horde Territory (i.e Durotar for instance) you weren’t instant flagged. You were only flagged for PvP in Contested and Enemy territories. Atleast in War Mode it’s 100% flagged at all times besides sanctuaries.
They just need to fix glaring issues with WM like sharding and it’ll be fine.