Pretty much all of it
Did the GP provide any specific reason why LN can't scale other than "here's a link to youtube from 2018?"
The author of the video was explaining how the LN works and it seems to be an exponential routing calculation problem ( similar to traveling salesman )
So while it could work for 75 k channels, it's not going to work for 1 million.
If the explanation of that video is correct (since you didn't disagree that), then how many channels it has now is irrelevant from my POV.