We run into some similar issues at CP. I think the ladder system is strange and the top group is usually 3 people if there are not an even number of people to have every group as 4. Three people groups have less point opportunities if you have a bad week! Sometimes I see the software has two people of a 4 person group go up and two go down. That technically means two people from group 1 could play 2 people from group 3. Carry that out a week and it could be two from 1 playing two from 4 that moved up the previous week. If there is a wide gap in skill, then this can be a huge point opportunity like your examples - cleaning up.

Part of the problem might be not having divisions locked sooner or that people can move down too much in groups - ex an A player maybe should not be in group 3 or 4 if you have 21-25 players. Where this may cause an issue is if you have someone new and start them off in the wrong division/grouping by too much. You may put them in A, but then if they get obliterated and have no fun, then you may lose them as a league player.

I think what happens a lot is someone in B does well and obtains a lot of points then eventually moves up the ladder enough to 'leapfrog' into A.

We have had many discussions where the conversation goes:
How did person X get so many points and end up in A? I only played him once or never the entire 10 week period and have been in the top two groups all season!

I don't know exactly how the software works, so I have no obvious solutions to offer.
You are not alone though. I can only suggest to look at the ladder and how/when it calculates and maybe look at division locking and group restrictions.

Does your league use bonus points and match points and do you understand how all of that is calculated? I don't know the ins and outs, but there could be some issues there too.

Good luck!