It's silently an unstable sort, which is surprising, and then to add insult to injury it's also slower. Yeah, I know, the C++ unstable sort is so slow it's slower than Rust's stable sort.
YMMV for input types, sizes etc but generally that's what the numbers look like and though it's not universal it's actually quite common. "I bet the C++ is faster" is the wrong instinct, sometimes by a large margin.
The problem does not appear to be in C++.
I prefer the C++ naming convention, because it matches my expectations. When I studied CS, quicksort was considered the default sorting algorithm, and stable sorting was therefore a special case.
My pet peeve is that standard library sorting algorithms are still mostly single-threaded. Multicore CPUs have been the norm for ~20 years, but standard libraries still don't offer reasonable algorithms for sorting large arrays.