You have to ask yourself why the library would become flooded & "unusable". It's an admission that you designed it like that. Why not design it better, so the user experience is just as good for huge libraries? I know that's a huge undertaking, so you could maybe say it's on the road map for early 2023 or whatever, rather than refuse to improve it at all.
This is many people's first interaction with itch. You could make it a better one if there was less of an air of stubbornness. Eventually the biggest "normal" itch users will have libraries as vast as the average steam library, which they'll have build up over time. As their library slowly becomes more unusable, you'll have to start working on a viable solution for this, rather than refusal on grounds that it's so far been designed to be unusable.