I would take that "advice" with a grain of salt. Think about this for a second:
You met a stranger and told him you use JS, and he told you to use Python instead.
Did he know the nature of the app? No.
Did he know the reasons you guys chose JS? No.
Did he know the platforms the app needed to run on? No.
Did he have specific, concrete examples of why Python is more scalable than JS? Doesn't sound like it.
Did he provide examples of a time when he tried to use JS for a specific app and then had to switch to Python due to problems with JS? Doesn't sound like it.
Yet he told you to change technologies... Do you see how silly this looks? Whether or not I'm pro or against JS, just based off of this alone, I wouldn't listen to this person unless they were able to articulate all of those things. These types of people exist in every environment. I don't think "JS has a bad reputation" as much as there are just people out there who find it fun to try and convince others of why they are right and the other person should be doing what they are.
I can think of 10,000 reasons to yell at him about why he should be writing his code in Rust instead of Python... But would I do that without understanding the problem domain, reasonings, history, culture, requirements, and provide specific examples? Absolutely not.