I've had some experiences with selenium and now I'm using puppeteer, and I honestly don't see the problem with JS. It's true that I have not much experience coding but it seems to me that Pupeteer + Flask serving ML to extract data is the cake. Also, being able to play around evaluating expressions in pupeteer, etc, makes it manageable.

Maybe I lack experience but I don't see JS being a barrier.

I would like to know what kind of string work are you doing. I can't imagine being dependent on parsing strings and such, that looks very easy to break, even easier that css selector dance.