Sigh dude, I don't think you are understanding me. Remove Pudding and what do we get from the story? Robin can be used to "move the plot forward for BB". Momo's dad can be used "to move the plot forward for BB". We know nothing about the three-eyed tribe other than them being able to read the poneglyphs where literally Ohara knew how to do, Robin, Saul apparently now does, Kouski clan knew, Oden knew, etc. Reading poneglyphs doesn't need some special race since we literally see regular characters being able to do that. We don't need three-eyed tribe, they were just created out of Oda's ass last minute to be used as a plot device.
Fishmen are directly related to the main plot due to the slavery aspect with the celestial dragon and because their island needs to be destroyed where it happens to tie with the redline which happens to tie with majorie, etc., you know main plot stuff. Tell me how does Three-eyed tribe directly tie to the main plot like that? There is nothing like that with three-eyed tribe!