Scoffing and thinking "hasn't this guy heard of Jupyter" says more about your attitude than it does the tool or its README copy.

Hasn't this guy heard of [old product that is a huge pain and no one likes]? Why would he ever make something that suits his own interests and preferences?

Yes, exactly. I'm sharing with this creator what my initial knee-jerk reaction was, admittedly exaggerating a bit. In case he'd like to avoid other people having a similar reaction. (And indeed, he thanked me for my feedback.)

It seems like you think that pointing out that I'm sharing my attitude is some sort of gotcha, but I'm confused. Sharing one's attitude is the whole point of posting an internet comment, isn't it?