Me too, but for me this is just a gut feeling. I guess the OP was more interested in possible justifications for a decision than the decision itself. Can you provide some reasons for what you have said? I would be interested too.

I personally would neither consider Python nor NodeJS for such a project if it was somehow time critical. The reason for this is that I don't know any of those enough to be confident that I could finish the project on time.

So the best advice I can give here would be: If you have a hard deadline that is very close stick with the technology you know better. Otherwise stick with the one that is more fun. I guess that you can resolve any performance problems in both technologies. And when your site starts to take off you probably have to re-write and re-design lots of your code anyway (I don't know where I read this first, but it was a startup that took off).