My understanding of compound time signatures is that they're distinct from others because they group notes into 3s (e.g. 12/8 differs mainly from 6/4 because it contains 4 groups of 3 notes, rather than 3 groups of 2; same with 6/8 vs 3/4, etc.).
The Pro Tools rulers don't seem to reflect that. Instead, for 6/8, 9/8, 12/8, etc., the dividing lines still group quarter notes into 2s or 4s, putting the emphasis on different beats. At certain zoom levels, it also puts a dividing line on the 9th beat specifically, which seems odd.
Attaching a screenshot of what I feel would make more sense, using 12/8 as an example.