757 Driver,
You seem to have missed to point of BA buying bmi (slots) in the first place.
Firstly, only a small proportion of bmi is domestic - and that proportion doesn't appear to be efficient, so combining it with BA will make it more efficient and free up slots.
Some of the other flying is competeing with BA, which can clearly generate more slots.
Some of the rest is actually financially productive ( or could be made so ).
Some is just unviable and will surely disappear.
A lot of slots can therefore be produced to change to crew greedy LH. Add in that BA have stated a very large number for desired recruiting ( double what all of bmi could provide ), and the viability of the deal seems clear.