Well for one, he's not the first to demonstrate it. There are a lot of other archers and speed shooters that you can simply type in "speed shooting" right here on Youtube and see them going at it.
Mongolian and eastern archery is still very much a thing. It's not a lost art in any way. The reason you see so many speed shooters use "much slower techniques" is because they aim for balancing speed and power with efficiency.
What I mean for this is that, for example, the actual world record for fastest archer still stands with David Powers, who shot 22 arrows accurately into a target in one minute back in 2000. That's around twice as many arrows as Lars shot off when he was simply blindly firing into the air for maximum speed.
The reason for this difference is because speed shooter looking from a practical perspective are trying to shoot in a way that lets them place their shots with more force at a longer range not simply for those factors, but also with consistency over time without failing to how much stress pulling the string back and firing over and over is going to cause.
The claim that Andersen can't hit anything over 60 feet away isn't all that bogus when you consider that he's firing by pinching the arrow or otherwise using the Mediterranean style three-finger grip and not a Mongolian style thumb-grip. Like in the other video commentary you talked in, neither of the grips Andersen uses compensates properly for the archer's paradox, making his shots very visibly veer to the side when loosed. The fact he punches forward with the bow in an exaggerated motion and doesn't lock the bow arm only makes that effect worse.
Fact is Andersen really does lack a lot in the accuracy department when using his modified quick-shot method. You can see that he switches off to a different style, bracing his bow arm using a longer bow, which causes him to fire much slower when he actually does try to shoot down range.
And again, for the "anyone can learn how to shoot fast like this, there are again videos that you can actually see on Youtube not only of people doing so, but showing you how. You don't even have to be all that good of an archer.
One such person being "The Bow Channel", as that person pretty adamantly goes over the process and explanations of matching Lar's techniques.