Linux is the most widely used kernel in the entire world. If you consider 'Linux' to be the OS, it is #1. If you consider all distributions that use the Linux kernel, it is also #1, collectively and individually (Android.)
If you look at the ranked list of Supercomputers, Linux has the entire top 500.
What the hell are you talking about?
Which, worth noting, does its own thing for init & services ( https://cs.android.com/android/platform/superproject/+/maste... ).
I think it's fair to assume they were talking about Linux as a desktop OS, which for some reason absolutely refuses to learn lessons from the other 99.9% of the market. And is also infatuated with internal fragmentation despite its tiny usage. That makes it really fun as a hobby for sure, and powerfully flexible for datacenter usages (from the mundane to the supercomputers). But also pretty terrible as a "I just want my laptop to work reliably & well" OS.
Which I had for the best part of 2 decades. Until systemd came along, infected pretty much every mainsteram distribution, and broke things that have always just worked like DNS.
Instead people decided "ooh mac is shiny, lets copy that". If I wanted OSX, I'd use a mac. If I wanted windows, I'd use windows.