Well said Water Check and had_enough.
I left CX for BA 3 years ago and it was the best move I ever made. With 200+ retirements per year and the 200+ pilots joining from CFE, if you don't get to BA within a couple of years you won't see a decent command before you retire.
Seniority means going where you want, when you want, on the fleet that you want. Don't hesitate if you're thinking of joining.
NB. One ex-CX FO got his command within 18 months of joining BA.