eJ does not have over 3,000 pilots.....circa 2,200 more like.
If you join via Parc/CTC then you go where they (easyJet) want you (LGW mainly I believe). If/when you are offered a full time contract, you can apply for a base transfer and go on the transfer list to await your turn.
That's how I understand it - if it's incorrect, I'm sure someone will put me right!