Yes. And that's why I don't understand your approach.
Right now I am reading millis() directly. So you could say I am also relying on the long-term accuracy of millis(). And while it's true that the ceramic resonator in my Mega is not that good, I'm also seeing drift in millis() with the Max32 which has a +/- 30ppm crystal.
Again - I'm not doing anything special with millis(). I'm just reading it. And it's losing time.
Why would your approach result in better time-keeping when it also relies on millis() ?