The Bassa V LGW debate has been done before. To recap, bassa suggested a no vote, LGW crew voted in favour of SFG.
BA committed to closing the regions, cabin crew, pilots, engineers, managers, ground staff et al. Bassa cannot be responsible for the closure, what they did do though was negotiate the best package possible for cabin crew to re-locate.
As far as I am bassa are not negotiating for mixed fleet so that point is also irrelevant.
I will repeat my consideration, and it is only that, in another way. Would I want somebody from mixed fleet to be negotiating my t&cs on 'legacy' fleet, t&cs which will not affect them. No.