All BMI pilots will join at the bottom of the seniority list in their respective seats - this ensures that no BA pilot is disadvantaged.
All BMI First Officers will have first access to vacated commands from ex BMI captains retiring or moving fleets - this ensures that no BMI pilot is disadvantaged.
Note - if ex BMI first officer moves fleet (I.e. goes to long haul for a bit) then their right to a former BMI command is void. So you will have to stay short-haul or lose your 'early' command opportunity but that is / was the current situation in BMI now so again your are not disadvantaged either. Seems fair to me?