Competition can definitely improve things, but it's not universally positive. In particular, endless competition in parts of the operating system makes it hard to build anything on top of them. E.g. if you want to distribute an application for Linux, do you build a Flatpak, or a Snap? Or take a more traditionalist approach and make RPMs, DEBs, etc.? You either pick your favourite and leave out a large fraction of Linux users who disagree, or you have to do more than one of these. This is definitely a drag on the ecosystem.
I agree that most users don't care about the OS, though.