CS, i asked if there were sources that state openly that the worse gehinnom a person has, the more olam haba he will have subsequently, applying the concept of yeridah letzorech aliyah.
The sources you mention say nothing of the sort. Only that Hashem is everywhere, even in gehinnom, which every single person who believes in ain ohd milvado would agree to, and that generally punishments are for the benefit of s person – again, the more stains, the more cleansing, but where in the world do you see that such a person will receive more reward? It’s not only without a source, it makes no sense.
Chazal say that “even” such people are filled with mitzvos like a rimon(i remember it saying this about empty ones, from the pasuk krimon raykasaych, as in amei haaretz – maybe it says it about poshei yisroel too, j don’t recall, but either way, it doesn’t mean they’re on the level of tzadikim!)
As for your example of yeravam, i addressed the issue of teshuva clearly in my response. Teshuva is something done in this world, the world of opportunity. Eisav could have been bigger than yaakov had he done teshuva, and yeravam, whose teshuva would have taught others more than dovids(see maharsha there) would have had more schar HAD HE DONE TESHUVA, but chazal say clearly that he has lost his olam haba because he failed to do so. A bechira decision.