That has always been the case. Consider for example, https://www.reddit.com/r/3Dprinting/comments/flpjcx/removing... from a few years ago where there was a situation and a number of the mods of the sub were removed.

The most senior of the remaining mods in there then became the top mod (note that it is ordered by activity in that graphic not seniority).

In what may appear to be a surprising coincidence, this is the same sub and it was three years ago that the current aggrieved mod got the top mod position by having others removed.