It requires experience.
A lot of those lessons only come after you've seen how much more expensive it is to maintain a system than to develop one, and how much harder people issues are than technical issues.
A CS degree, or even a junior developer, won't have that.
Whether Python will be easier or harder to maintain depends on numerous factors that vary so much for each job that you cannot generalize upon.
That's something experience shows.
Reaching such a conclusion that "Python is not a right tool for web backend" is just naive.
No matter how experienced a developer is, reality of the world is at least 100x more diverse than what they alone could possibly have learned and experienced.
If one believes to possess the experience of everything to generalize on complex topics like this, it just shows this person could benefit from cultivating a bit more humbleness.
But I disagree on "not the right jobs for the tool".
Python is extremely versatile and can be used as a valid tool for a lot of different jobs, as long as it fits the job requirements, performance included.
It doesn't require a CS degree to know that fitting job requirements and other factors like the team expertise, speed, budget, etc, are more important than fitting a theoretical sense of "right jobs for the tool".