I know the issues, I've never been majorly into PvP but I was addicted to a huge factions server for around a year once. Strafes, trying to anticipate where your opponent will strafe, a lot more complicated nonsense.
I just also think at this point, its been years, and several full versions of the game have come out since, and its time for people to just accept things and move on. Just in the context of Massive, knowing most PvPers use 1.8 means World Staff are majorly limited in block choice, since a lot of basic things like Barriers weren't out yet, same for so so so many blocks. Bone blocks, concrete, now all the corals and new slabs, etc. Even Hypixel has basically handicapped itself by appealing to the older versions, with a lot of blocks and things that would be good tools for their minigames going unused. And a lot of mods still have to try and keep their old versions up-to-date and functional on older versions.
In general the divide really just makes stuff way more annoying for way more people than it would be for just pvpers to switch over.