You're right. Python and ruby (and Java) have very good libraries. However, while other people's libraries are very good at solving problems other people had, they're not very good at solving new problems, and the fact is that all problems are new problems to a beginner.
This means that while people who learn on python and ruby (and java) tend to be able to accomplish something faster, they don't generally become very good programers, and tend to stay inexperienced (or rather nonexpert) for a very long time- sometimes a decade or longer.