I disagree, but okay.
Correct.
Also correct, sort of.
Yes, whether a raid exists or not doesn’t mean PvP will or will not happen.
However the more the PvP population is split up (whether into separate shards or separate queues), the harder it is to find good battles in the open world and the longer queues take for instanced PvP (rated or otherwise).
So when you have 40 Alliance in a raid on one shard, and 40 Horde in a raid on a different shard, that is taking 80 players out of the good open world battles and out of instanced PvP queues.
You say this, but you also say you hate instanced PvP and won’t do it regardless.