> made CLOCK_MONOTONIC unclear in this regard
I don't understand what you mean. Doesn't smearing still mean the clock only goes forward? It's still steadily incrementing. The only difference is that a second is slightly longer/shorter than you expect, but you already have to account for that if you're doing the kind of physics experiment where it would matter.
If you have one event per millisecond then you get 86,401,000 events on a day you smear, and that’s inconsistent with the 86,400,000 you get on days either side.