Ok so where is the line where a bowler who clearly seems worldclass can play enough to be rated ahead of someone good who played 130 odd tests?
Cummins at 43 tests is fine, but Bumrah and Harris at 30 and 27 tests are not? At least admit its a personal arbitrary judgment call.
Once again, you are not following Kapil's career rightly. It is not a case of averaging around 30 all through his career. As mentioned earlier, he had 2 clear phases early in his career where he was bowling at ATG levels.
Phase 1 : 27 tests - 118 wickets at 23 (1979 Jan -1981 Nov)
Phase 2: 19 tests - 80 wickets at 23 (1982 Dec - 1983 Dec)
Those are 198 wickets at 23 across 46 tests in just 2 phases. Harris hasn't done close to that much in his whole career though he was at a similar level when he played. Him being thrash early and not playing anything at that time protected his average as PEWS mentioned. You might be thinking I am cherry picking, but Harris's international career was exactly that (started at a period when he was bowling well at a world class level, after a struggle with fitness, and ended at a time when he longer could bowl substantially).
Kapil was meh outside his peak phases, but the proposition is that Harris would have been worse, by eye test, had he played that long.
Cummins has already played as much as the above peak phases as Kapil and done better, so he is clearly the better bowler.
I would say the same about Bumrah as I said about of Harris, except that he hasn't been thrash at any point and also has a phase ahead, so he could go ahead of Kapil in the near future.