Do you thing an employee rep (branch official), should lead or facilitate?
A rep should do both. As the job title suggests, they should "represent". Therefore they need to ascertain the general will of the members who they purport to represent. They then act as facilitators of that view with the employer. Then, following whatever discussions they are mandated to hold and within the bargaining structure agreed with the employer, they report back to their members and give their opinion on the best course of action to take, ie they lead. Only they can perform this task, as only they have access to all the information and nuances picked up from discussions with the employer.
I think the flaw in your original enquiry with respect to BA cabin crew representation is a very simple one: the current branch leadership simply has no mandate to fulfil either (indeed any) role on behalf of members. They decided to suspend all rep elections until the dispute was resolved. Therefore the current reps cannot fufil their obvious role (ie obvious because they are called "representatives"). And let's not forget that they do not actually know who are members, if the issues surrounding the latest ballot (and the first strike ballot) are to be believed. It's hard to be representative when you do not actually know who it is you claim to be representing.
At the moment BA crew have two equally unappealling choices of persons to act on their behalf: the incumbent Union complete with "reps" who refuse to put themselves up for election/deselection by their (dwindling) membership; or a new group (PCCC) who are entirely anonymous to the vast majority of people they wish to represent and ask to be accepted as some kind of act of blind (literally) faith. No wonder BA isn't talking to anyone. With the best will in the world they cannot actually find anyone who they can be sure has any kind of authority to speak on behalf of crew. We know, for instance, that the full time leadership of Unite cannot fulfil this role either, given the various agreements made and then sabotaged by the individual crew branches.
So here's a question for you. Put yourself in the management position at BA. Who would you call to try and resolve this dispute? The branch leadership (not subjected to electoral scrutiny for quite some time, several reps no longer qualified to be such by virtue of terminated employment); PCCC (not sure how BA gets to do this, presumably some kind of MI5 dead letter drop as the "leadership" is known only to each other in the kind or organisational structure so beloved of guerilla organisations); Unite's full time leadership (the people with a general lack of awareness of who actually is in the Union)? Or would you just talk over the heads of the lot of them, engage with staff directly, and not bother with collective bargaining which is clearly not delivering results for either staff or company?