I suppose the complaint was to hint that mathematics that is older than 50 years is too old for modern tastes, but most of our modern notation was already established at the start of the 19th century. Even Euler uses almost completely modern notation, about 250 years ago.
Oh, I didn't even notice that. I encounter that notation frequently enough, but it wasn't the one I was taught in high school. Kind of hard to do a web search for its origins. I tried and failed.
I recognized it immediately but each math teacher I had in college used different notation for the definite integral. I really did think it was common. I need to study more math.
I suppose the complaint was to hint that mathematics that is older than 50 years is too old for modern tastes, but most of our modern notation was already established at the start of the 19th century. Even Euler uses almost completely modern notation, about 250 years ago.