no is not!
and copying code from libraries does not mean copy/paste from stackoverflow, but reading some code and understand what you need.
i'm sorry but if you are going to copy the entire library, then just add the dependency.
If you are going to read and just add the part need it, then you are a good developer.
Great developers stay curious and keep learning for passion, this is the only way to evolve.
Bad developers are just not curious and very lazy. They will add a library that one feature that they need, or even worse some time is just a few lines of code written in an old version of the language as a workaround, and now is implemented directly into the language. I have seen this so many times that is just sad.