Pardon me, but your implementation is a strawman. Pick on this (which doesn't require Cython 3):

    from libcpp.vector cimport vector
    from libcpp.pair cimport pair

    cdef class PointVec:
        cdef vector[pair[float, float]] vec

        def __init__(self, points: list[tuple[float, float]]):
            self.vec = points

        def __repr__(self):
            result = ", ".join(f"({x}, {y})" for x, y in self.vec)
            return f"PointVec({result})"

        def __setitem__(
            self, index, point: tuple[float, float]
        ):
            cdef pair[float, float] *p = &self.vec.at(index)
            p.first = point[0]
            p.second = point[1]

        def __getitem__(self, index):
            return self.vec.at(index)

Nor can you prove that a language is error prone by providing a 40 line example written in an antiquated style that deliberately avoids using the safety features at one's disposal.

Okay, get specific. What in my implementation requires extensive experience, or where was I unreasonably thorough?

This assertions is representative of the myopic one-dimensional think of rustaceans. It only makes sense if the only thing your care about is safety.

C++ isn't what I would call a fundamental limitation.