I guess it's well known if you use either platform, but I can see it's not obvious to someone new to the fediverse and trying to understand it from the outside.

Hello from PieFed!
Kbin/Mbin is actually very versatile, it has a threads side (much like Lemmy), but it also has the Microblog side which is like Mastodon in form and function. One or other of these usually works for most of the fediverse.

I agree, it is not calculus, it's trigonometry.