The concern with pay-to-skip-grind revenue models isn't so much with any notion of "fairness" or "integrity" as much as the fact that it greatly incentivizes as

The concern with pay-to-skip-grind revenue models isn't so much with any notion of "fairness" or "integrity" as much as the fact that it greatly incentivizes asshole progression design which typically manifests itself in the form of intentionally-way-more-grindy-than-necessary midgame/lategame progression pathways. Designing the ideal rate of progression to keep a given game engaging is difficult enough as-is. Too little content gating and you risk burning through all the content too quickly and players getting bored. Too much content gating and the grind begins to feel punitive. In this context, muddling the mixture further by throwing in this kind of incentive just feels like a recipe for shit-tastic UX/CX.