We've seen each division (slightly modified) as its own league though in 2020-21. And the weakest "league" in that setup, the Canadian Division dominated the top of the scoring table. Not to mention that your Connor McDavid example falls apart there, because he was uniquely dominant in that setting. He outscored the closest non-teammate in the league by 52%. As good as he is, that's not even something he does. If he were doing that as a course of normal business, we'd be talking about him with Gretzky.
To give a comparison, had he outscored 3rd place by 52% in his 152-point season, third place would have had 99 points. In reality, that tied for 12th. No, you're not going to convince me that giving a weaker league setup didn't inflate the best. I can listen to an argument that the 60s were stronger. I can't listen to one that the 50s weren't strong, because the facts simply don't bear it out.