As HF has implied:
Whoever those "several people" are, they don't know what they are talking about I'm afraid. Whichever fleet you join on, you MUST expect to be there 5 years.
Eqyally important to remember is this: Whilst it is called a freeze, actually BA can do WHATEVER they like with you in your first 5 years! Not very long ago, a small group of pilots joined on the 747, only to be directed a very short time later to the 777!
Due to the differing route structure, and trip lenghts, some of them were EXTREMELY distressed!
Buyer beware! You really do have to want to be in BA, and NOT on any specific fleet, base, or routes!
But if you prepared for the interview, you knew that already didn't you!!!