I think we’ve reached a real cross roads with the card hobby/industry where the common/mass-produced stuff (YGs in hockey and the like in other sports) is going to start falter. However, the truly rare, high high end stuff is going to continue to increase (and could increase significantly) in this social media and “look at what I have” age we live in.
I view it a lot like art though. Often times the value is what someone is willing to pay for something. However, like art, you can encounter situations where there’s a high valued card/piece of art, but no one willing to buy it at that price it’s valued at.
I think you could include things like a high grade Orr rookie in that high high end/rare category, but do think you’ve overlooked the rare modern cards and peoples’ recency bias + desire to collect/invest in guys they’re watching play currently. With that said, I agree that UD has pumped out so much McDavid stuff (including high end like a cup tribute for every rookie year) that makes it not so rare, which will definitely hurt the value of a lot of McDavid stuff in general.