Last time I've tried Jupyter, about a year or two ago, the user experience wasn't even close to that of Mathematica. I guess I'll give it another chance, but can you tell me in what way Mathematicas notebook interface is outclassed, in your opinion?
The only major beef I have with Mathematica are its default stylesheets. They suck, every single one of them. There is no good distinction between input and output fields. Whenever I install Mathematica, the first thing I do is to make the "Natural Color" stylesheet [1] the default but unfortunately, it isn't even present in the options anymore since a few versions ago.