Yes and no. System call level line gave us few quite popular full-blown OSes (not just Android but also NAS systems, wifi-routers and so on).
But it's also easy to see that only OSes which define yet another layer are successful among non-geeks.
This strongly hints that both levels are important: system call level for OS builders and another, higher-level one for application/hardware system builders. System where you can mix and match everything (see Debian or any other desktop distribution) is embodiment of mediocrity: it does a lot of things, basically everything you can ever imagine. The only problem: it does everything equally poorly. Conflicts among the low-level plumbing components are more-or-less constant and system often breaks in strange and usual ways. These things are relatively easy to fix (symlink here, small config file there and everything works again), but it's not something Joe Average can do and it's not something Joe Geek wants to do.
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