The way to penalise the new arrivals is through a significant type freeze, perhaps 5 years.
People need to realise that an initial freeze is a temporary measure that solves nothing.
There were guys that were a month or two ahead of me in Oxford who joined BMI shorty before I joined BA. I'm (significantly) more than 5 years away from a long-haul command so by your logic the BMI guys who join BA today get a shot at a long-haul command on a 747/777/787/A380 before me. As anyone in BA knows, a few places in seniority could mean literally years (no exaggeration and not that unlikely either) in the wait for a seat/fleet.
You may find that acceptable but I know about 3300 people who absolutely do not.
The current career prospects of BMI pilots will be protected (with the exception that their new airline isn't on the verge of bankruptcy). But a BMI-DOJ based place on the BA-MSL isn't going to happen. The BACC/BA will see to that and they'll do so entirely within the confines of the law. If the BMI-CC are interested, the BACC will help them get good a deal as possible. But not one that disadvantages BA pilots. Everyone needs to have a serious look at what their career prospects were a year ago and factor that into what they expect them to be a year from now.
If you have issues with the fact that thats not how BMI/BMED was handled then I suggest you take it up with the BMI-CC/BALPA.