The two criticism at the end are... odd.

First, there is criticism that assigning to a shared_ptr is not synchronized so it would be bad to share a single shared_ptr object between threads. True, but that is no different than literally every other non-atomic object in C++. It's not surprising in any way.

Second, there is criticism that assigning to the object pointed at by the shared_ptr is not synchronized between threads. This is odd because that's not actually different than a single thread where there are two shared_ptrs pointing to the same object. That is, even with single threading you have a problem you must be careful about.