Yes, exactly. That's what many people who admire the two don't want to hear: Their unreal stats partly stem from the exceptional roles they played in star packed super squads. Sure, they justified their respective status through their quality but in the end it definitely boosted up their stats in a way that most likely would not have been possible in previous eras. It's context that doesn't take anything away from their class and accolades but people who only look at goal stats and want to compare them to put their idol on a pedestal don't like that.I also think there is a type of greed in the way they play at the moment too, not really helping their team-mates, for example in Ronaldo's case, he never gets injured.
But his risk of injury is so low because he never makes a tackle or gets in a difficult situation where he might pull up. In Ronaldo's head, an injury = a few months out = risk of not scoring. Compared to say Cavani who will run all day, but will risk injuries and pain. Ronaldo doesn't risk any pain because it will hinder his quests for goals. Messi is similar. What's also interesting apart from their scoring records, is their appearances. High-intensity forwards are not supposed to be breaking appearance records like they are. The reason they are is because of their complete lack of effort off the pitch. It's conserving energy so they can profit in very specific moments. It is in a way a selfish style.
As said in my initial post, I think the real question is if these exceptional roles are still worth the costs, not if the two have fundamentally regressed that much physically. Right now, the teams at the top are very cohesive and they don't feature players who don't have to press. But this might also be the case because those teams don't have the money to shoehorn these players in. Who knows how good City would be with Messi in the squad. They could be better or they could be worse. Or vice versa: Do Messi and Ronaldo look like they have regressed because they actually regressed or because their roles are outdated/their squads aren't as cohesive and superior as they used to be?