I think the problem is - and this is a criticism of the wider movement to change the language, not of the RSSB in particular - that the change is being forced on people, not all of whom wish it.
Someone - particularly an older person - who uses the term 'manned' is almost certainly not trying to be offensive or exclusive: They are simply using the language that they have been brought up to speak. For example, to me, the term 'manned' *is* completely gender-neutral, and can apply equally to a man or a woman - because that's how the English language that I was taught and grew up with works and it's therefore how I speak. Someone who insists that the term is somehow exclusive is quite simply failing to understand the meaning of the word. Now if that person or any other individual prefers to use the word 'staffed' or 'crewed' instead, then to my mind that's totally fine: In the end, as long as your meaning is clear, it seems reasonable that people should be allowed to use whatever words they are most comfortable with, and we ought to respect that.
But that respect needs to go both ways, and at the moment, in much of our culture, it doesn't. I totally respect the right of anyone else to use the word - say - 'crewed'. But the impression being given is that there's no equal respect for people who prefer to say 'manned' (which in most cases will be simply because that's the version of English that they have always known). Effectively, people, particularly older people, are being shamed for doing nothing more than speaking the way they naturally speak without any ill intentions. That is at best unkind and at worst discriminatory towards many older people.
Now of course, unless anyone here was actually involved with the particular RSSB changes that we are discussing, it's impossible for us to know the details of how/why they decided to make those changes. But it certainly does seem to be part of that same movement towards dismissing the language that many people have always used. And if that is the case, it is concerning - quite apart from the issue that time has been spent (wasted) on making a change to rules whose meaning - presumably - was already perfectly clear.