I fly for a foreign carrier and am an A330 capt. If I get hired by Delta,
from reading on here, the preferences are based off of the last four of your SSN. Just to confirm, if you already have an A330 rating and then do not get assigned an A330 Capt in my drop, there is nothing I can do, and will just have to learn to fly the 737 FO or whatever assigned? WTF???? 
I'm kinda being snarky, but "Come on man". If you leave the ULCC and go to any major airline, you will take what your new seniority entitles you to as far as bids. You leave your previous life at the door as far as bidding.