Saying Linus uses something is just appeal to authority by the way.
I was giving Linus as an example of a member of the Linux community, and a particularly prominent one at that. There are many indicators that Fedora is well regarded, and that is just one of them.
you either adopt them or it becomes increasingly difficult to run software on your distro.
Arguably, systemd made it easier to run software on Linux. The standardization made it easier for devs to write software that worked across distros. Devs didn't have to fight fragmentation in the lower levels and could focus on building platforms on top like Flatpak, which in turn led to even more software and apps available on Linux. It's way easier to find and run software than a few years ago.
I'm guessing what you were trying to say is that it's harder to find and run software on Linux that doesn't use systemd. That's fair. Just like it's hard to find apps nowadays that don't use web technology, and require something like Electron or Firefox to run. But if we think of systemd as a platform (though I think it's more complicated than that), does it go against the ideals of Linux?
The fundamental Unix principle is having small programs that do a single thing well and that can be composed together
First off, I know you didn't say this but I want to just clarify: software principles are different from community ideals. Software principles are a means to an end. And they are often broken. Modular design is hard to get right. Microservices often end up messier than the monolithic approach. Ultimately it's a balance. And strategy plays into this too. If monolithic design allows faster iteration, then even if it gets replaced with modular design later, you can use the lessons learned during those iterations to make the modular design.
It's possible that someday Redhat tries to weaponize systemd and it ends up holding Linux back until we can replace it. But I doubt it. If you look at the recent backlash that Fedora and Firefox has gotten for AI, you can see that the Linux community is pretty vocal and active about their ideals.