88 for me is not about being picked off by one so much as it's taking a potential player out of the action. They’re sitting in a gun with their fingers crossed that they hit. And if I’m fighting another player and one of us just got popped by that lucky shot, two people have just been denied their fun. It’s a grief weapon IMO.
I find it hard to describe a totally immobile weapon as a griefing weapon. It's not that's a sudden airspawn opens behind your back

But more seriously, and only speaking for myself: I have quite a number of kills in all kinds of manned guns, but I guarantee you that almost all of the time I would not suddenly up a plane if the gun wasn't there. Because I mostly use guns if no other option is left - jumping to a CV when the bombers are already there, log on to a remote base that's already vulched. Or I can't due to real life constraints, for example eating something

And as far as griefing goes, about all players I shoot down in a manned gun are attacking the base. Deacking, vulching, bombing my CV. Two players having a noble duel in the skies are usually way outside any reasonable gun parameters.
And finally, the percentage of fighters shot down by manned ack is really low, considering the 6% number is mostly made up by bomb trucks and similar attackers. And the 88 has only a tiny share of that 6%