This post and my own post a little below it in the same thread add a little anecdotal weight to your theory.
Argent Dawn has certainly been suffering very badly with the same problem: good framerate, good ping but still a huge lag when interacting with the game (pressing abilities, interacting with mailbox, bank, portals etc).
The same thing has been occurring in some (but not all) Epic BattleGrounds, too.
If this is actually a thing, let’s really, really hope that they fix it without messing up Argent Dawn’s RP non-sharding, which is vital to the lifeblood of that realm.
It would be a bit hypocritical of them to make a big deal of Ibelin and to then shut down the system that currently enables the existence of that very same type of RP.