Ignoring the personal stuff in the rest of the reply I think the above gets to the route of the problem. I think we all assumed you knew you were on two inflexible tickets, you didn't and so you have sacked the person responsible, that sounds like the right outcome.

If you are sure they didn't try to get volunteers to get the later flight you can carry on trying to get BMI to take responsibility but it seems unlikely. As others have said the guy in front of you may have been on a flexible ticket and/or have status so there is no definite reason why they should have offloaded him before you, although it would have been nice if they'd asked.