Battlegrounds cross-realm matchmaking

I was wondering how does it work. Went through numerous threads and didn't find answer or solution.

Is this normal? Is there a way to avoid it? Blackrock average item level 250+ characters(checked their armory during the BG), consistently playing against Icecrown and Lordaeron 3-4k gs characters?
On the other hand I often get matched against 90% blackrock players battlegrounds on my priest with average item level 210-215. The few times I luckily enter a mostly Icecrown BG, there are still some highly geared Blackrock players.
Unplayable.

https://i.ibb.co/0jY8DZyh/Wo-WScrn-S...526-045427.jpg

That guy seriously destroyed y'all