TL;DR for this question:
Yes, JUCE was written way back in the old days, when the standard containers were really unsatisfactory, and most libraries rolled their own container classes.
Since C++11 became a thing, our advice is that if you can use the new standard, then you should prefer things like std::unique_ptr, std::vector, std::array, etc. The JUCE equivalent classes do their best given the contraints of c++98, and some people will probably always prefer them for various reasons, but the new standard library is probably a better choice in the long-term.