when you create a process, no matter how good you are, you still have to read from the task image (in out case, let's say an exe, talking about the old "hellow.tsk;1" - reading from a secondary storage cannot be faster than secondary storages (hdds) allow. which means creating processes is naturally slower than creating threads. this was the basic idea and the main reason for wich the thread switching model has been used. now, there are side effects, dead locks, race conditions, etc but i still think it's worthy! that's why modern unices (and the posix standart itself) mention about threads. fibers are another story, but mostly, the peformance boost is coming from being able to naturally cache (implicitly discard) unnecessary secondary storage reads. a kernel architect knows that, regardless the kernel.
now, what is more interesting is the (aprox) statement "when it comes to symetrical processing we do play with priorities" which means that the scheduler might be hardcoded somehow (have a huge special cases global "symbol" table of some kind) - well, the video is great (i wish you didn't "revised" the third episode) and it would be even greater if low level engineers (from production environments) could access kernel source code, at least in fragments, under strict nda!
despite is great to expose your kernel at least to students, it makes very little sense to limit kernel visibility to schools. a lot of (actually the BEST) engineers, even they are not working at microsoft (but for microsoft, indirectly) would take huge contructive proffit from being able to see all kernel objets (and algorithms) in source code (it doesn't even need to be actually buildable)
so, if the intent is to be customer centric, trying to provide each customer the best of the best of the best, you should create a new program, where a certain (low level enough) engineer can say "hey, this is who i am, what i do, i think i need to see the kernel, under strict nda, send me the source code, for, let's say, scheduller)
i am super confident that (no matter how strange may sound today) will hapen tomorrow, hopefully in our live times!