I don't see Modern C++ ever getting past its safety-third design.
Oh yes it is. std::vector is hella legacy. That's not a C++11 addition (where "Modern C++" began). And it has all sorts of very-legacy warts like https://en.cppreference.com/w/cpp/container/vector_bool
"Modern C++" added std::array which is what you might be thinking of, but it's much more limited & targets a different usage.
If it is, it should throw a warning that it's deprecated and have a replacement for it.
Because other have not aged well. String is heavily optimized for single short size. Which is almost never a tradeoff that matches your size. Hash things are strictly worse in std. Node based with allocator are not for high performance.
Of course people use additional array types that have short buffer sizes that are needed and such. But vector is probably the last usable std container. Gaming where i work has some extra requirements that exclude even vector but i think i gave you overview.
The argument was "this bug exists in pop_back, therefore Modern C++ is a failure" which is nonsense. This pop_back behavior predates "Modern C++", so it cannot be used as a reflection upon the current trends.
Take std::span which didn't even exist until C++ 20. Surely that's a modern feature and is safe by design right? Who would add a feature to a language they wanted to be safer five years after Rust and yet make it unsafe by default and even remove safer options "for compatibility" ? Ah yes, WG21.
The scenarios where there is no option in tooling (C vs C++ as only options), we have to keep using C++, for others, we can replace one domino piece at a time, eventually only those niche scenarios will be left.