Trust me Manutd 1999 by the time your career has reached a stage that you need to worry about whether you are "stuck" on a 330 or whether the chance to move to the 787 is an option you won't care.
By then it is all about money and lifestyle.
Personally I would rather stay on the bus as I like my cheeky Caribbean trips mixed into LHR stuff but more importantly the thought of 3 weeks ground school plus 12 sims plus line training fills me with dread. Too lazy/lifestyle focused to worry about it. One day you will understand where I am coming from, but as someone who started off sweeping the hangar floor and towing gliders I understand your simplistic view on your future career. I was you once. If the fleet manager rings me up tmrw and says "your off on a course next week" then ces't la vie. I think Wireless is coming from the same wavelength.
All the best