Companies have a problem with adding members they know can't fit the group, WinWin's case is different, I don't think he fits NCT's concept at ALL, and it was stupid to add him because it's obvious there are a lot of members that can sing, dance (kpop dancing), rap, better than him. This is not to bash win win but SM made a mistake in adding him because he can't contribute anything to NCT, they don't promote him as comedy relief, they don't promote even in his dancing, they promote Ten's dancing skill more than his, the thing with Ten is that he can dance hip hop better than Win Win so it's easier to promote him.
Companies like to add filler members but not do anything with them after. Just leave them and not give them lines, then why did you add them in if their talent is not up to par? It's bad for the idol and the group because now people complain about said idol getting no lines or screen time because the company made a poor choice.
I agree, but, it may be a controversial opinion, I never thought of Win as a filler member, he was added because of his dancing and more importantly because of his pretty face and that face made it work in 127. It was stupid that they were so quiet about his departure but whatever.
Oh and let's not be naive. Companies sure know how fans are complaining about lines, that creates a lot of buzz and that's important. Some may even continue giving less lines to a member for that reason before they decide it's enough.
And let's not forget that some idols have their own problems: anxiety, lack of confidence, language skills when foreign members are concernrd, and that prevents them from wanting to be in the spotlight that much. In that case fans nagging for more lines isn't a good thing