OpenRC does the same stuff as SystemD (without uDev) and OSS does the same stuff as ALSA, including simultaneous audio output from multiple applications. If they really wanted compatibility, there's no reason they can't fix that.I don't claim Linux is innocent, either.
Also, I'm mostly ignorant on which approaches those follow. If the change is actually needed, the approach is really different and the goal as well, then maybe it's not an unnecessary breakage. As for Mir and Wayland and the several toolkits (well, only most of them), the goals seem to be shared, and in the particular case of the display servers, there doesn't seem to be significant difference on the approach, aside from Mir being a server (while Wayland doesn't mandate it to be that way, but gives you the freedom to) and doing server side allocation (same clarification for Wayland as before). I understand the difference between GTK and Qt for being a licensing issue, and at the time GTK started Qt was proprietary even. I, too, see the reason for FLTK, since this does differ in approach, trying to prioritize lightweight, while the rest try to be feature complete (this doesn't mean they are willing to waste resources, but they will prioritize features over frugality).
As for the competition, being loved and being healthy are two different things. I agree most people on the community love to compete. This doesn't make it any healthier for the ecosystem. In situations it is (different approaches might fit different users), in situations it isn't. I don't call it competition when goals and approach doesn't overlap, and that's why I can generalize competition is not healthy on open source. But having multiple solutions, if the approach and golas are significantly different may be a good thing.
EDIT: I just realized I completely misread your post. My correct answer follows.
Maybe it's true. But ALSA, I believe (I'm not really that into subject, so I might be wrong) is there to solve lots of problems. On upstart/systemd, based on the fact I toyed a bit with their configs, make it far easier to make a concurrent startup, so again, is not a breakage "just because". What I meant on the other point was actually hostile breakages, aimed mostly to break compatibility with everyone else. I don't know which the licenses are or if they depend on very specific Linux features, though.
What I do know is that apps don't usually rely on init systems nor are they aware of them, so it doesn't really break compatibility, and just improving owns system doesn't imply competition, but just looking for new features. With ALSA, I have to admit in some cases they do, in other cases they just use OpenAL which in turn chooses an available backend. ALSA I'm aware is GPL, since it's inside the kernel, and is likely to depend on Linux specific features, since there must be a reason why "Linux" is included on its name.