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    This sounded a bit weird:

    XDebug is a debugger that can do coverage too. PHPdbg is another alternative to X-debug. Pcov is built for PHPUnit code coverage not something else.

    but the explanation indeed is that pcov is small and strictly built for code coverage whereas the first 2 are actual debuggers, that is the reason for the speedup. Yes, it’s kinda written there but I still wasn’t sure as I hadn’t heard about pcov before.