PHP doesn't have arrays, it has hashtables. Although PHP probably got there by accident, consensus in dynamic languages today is that the hashtable is the superior default collection datatype.

The standard library is state of the art in C, which is most of the time state of the art, full stop. The interfaces to the libraries are awful by way of being inconsistent.

Performance is more than good enough. Scaling it properly is more of an artefact of good application architecture, but this is the case for any environment.