Yes, the biggest available library is big, that's hardly an argument though.
A really common library that gets used in every project for common use-cases is big.
It's a very good argument.
No, saying "one common library is big" isn't a good way to show that "Python dependencies are big", which is what the initial claim was. Most libraries are tiny, and there's a very big one because it does many things. If Tensorflow were in JS it wouldn't be any smaller.