Yeah I’ve noticed this, too. Vintage isn’t really dipping anymore. More or less, it has stagnated. I also pointed out the parallel to 2016 through 2018 as you did in your No. 2 point.
Even before the boom in 2020 which was accelerated due to a variety of once in a lifetime factors, things were starting to appreciate in 2019. I remember during the summer of 2019, WOTC holos were seeing some movement. Nothing crazy, but they were increasing in price. Those who were around at the time probably remember this.
I think the line that needs to be clearly drawn is the difference between graded and ungraded. This is a great time to be buying graded vintage cards. Ungraded is another story. While there was still a decent supply of raw mint WOTC in the couple of years following the Pokemon Go boom, that supply has dwindled to almost nothing now. As I said earlier, any listings for near-mint WOTC holos on eBay are almost always PSA 7-8 quality at best, but they are going for close to PSA 9 prices. That makes raw a tough buy right now, and it also make flipping a very difficult thing to do, which I definitely think is a reason so many people are down on vintage.
Let’s face it: many people in this hobby are flippers, and while there is nothing inherently wrong with that, they are naturally going to have a bias for cards they can easily buy raw, grade and make a quick buck on. You can’t do that with vintage right now, and I’m not sure you’ll ever be able to do it with vintage again. I mean, it was even relatively difficult to do that in 2017; let alone now where the raw mint supply has been swallowed up.
This might represent the best time to buy graded WOTC. There will be another spike in the hobby at some point. Will it be like late 2020? No, but prices will increase again, and we will all eventually end up having this same discussion again.