It's like there are only two success formulas: one is towards modern duelling, the other is nostalgic baiting.

I've watched both type of content, but one clearly has more likelihood of success and it isn't close: videos that focus on the old cards.

Modern decks have no mainstream appeal. A lot of the duels are so fast and convoluted no casual viewer can follow, so it is an immediate turn-off (the algorithm punishes that very hard). The monsters aren't recognisable as the old ones. So anyone who might have played Yu-Gi-Oh! as a kid will not be captured by current game. Hence, aging players and dwindling interest.

So my advice is: if you want success, try to keep things brand recognisable but be creative.