What would people say if Microsoft said “yeah, we’ve allowed windows to languish in recent years.”

Well, I think they did let it languish, if looking at it being enshittified in recent last ~10 years. Also, it’s not their core product anymore. Almost nobody buys a windows license anymore, because piracy was already high, and they let you keep your license from the previous version so whether you had one or not, most probably now you have.
I think Microsoft’s core product has not been windows for a long time, but their cloud services, and maybe office and the other common business tools.