We see a lot of fans and pundits make the mistake of assuming progression is inevitable in the future when a young team exceeds expectations in a single season. But as you adroitly point out, that's often not how it works. Regression is a harsh mistress and more often than not the more difficult task is maintaining and growing success than achieving it to begin with. And the way this season ended should raise a bit of a warning sign regarding that. If you count the Atlanta game last night, the Rams finished the season going 2-3 in this last 5 games.
So, what McVay has done is set the stage. He won the first battle overall but the harder work is now in front of him if he's going to win the war. And he's not going to have the luxury of taking anybody by surprise or being taken for granted going forward. The opposition is going to spend an off season figuring the Rams out now and Atlanta may have provided the blueprint. Make no mistake it's going to be harder to be good next season than it was this season.
Can they avoid regression? They'll need to be better than they were this season if they hope to. Can they additionally take it to the next level? Hard to know at this point but this is what I do know. Whatever happens, it's going to be a darn sight better than it was the decade leading up to this season. And I wouldn't bet against McVay. I'm just looking forward to seeing what he does next, and that's so much better where we've been for so long that I'll take it!