While I will agree that older games were on average more difficult than these days, blanket statements like this article suggests are always gonna be inaccurate. Why we say that games of yesteryear are better is not because they were more difficult than today. They are less fun because when we were children, impressionable and with vivid imaginations, those old games shaped us in more ways than one. They shaped the type of gamers we all became. They shaped and influenced us to like certain things, and in many cases become the type of person we are today. When you are a kid, everything is more magical and fantastic than when you are an adult. Today we have to content with the jaded negativity that comes with being an adult. That is why games in our past is more fun. Most certainly not because they were more difficult. Fine, sure, you may have loved the challenge as a kid, but there were more than enough easy games out there.
At the end of the day, our child minds made the games we play into these fantastical, magical worlds we got to escape into. They shaped us at a young age and made us the gamers we are today. Not because they were difficult, but because they gave us an escape into a digital world of imagination. Today's games are objectively more complex and overall much better than in the days of yesteryear. But we have lost that ability to look at the new games through the eyes of a child, and be filled with wonder and excitement like a child gets. The world has pushed us around way too much.
So, while I agree that games are easier today, I really don't think that is the reason why they were more fun.