Yes, the article covers this (mentions the std::variant). This makes it a closed set though. Other differences is that your Event here is as big your biggest event type, and it doesn't go through normal inheritance mechanisms. With polymorphic you could just have an abstract Event and implement your subclasses normally.

A way to see it is some sort of type-erasure over destruction and copy-construction (plus another corner case for mismatched allocators).

The constructor of polymorphics captures the type of the subclass during its constructor (they didn't make the same mistake as with shared_ptr of giving it a pointer constructor, like the UB in case the destructor is not virtual in Base *b; shared_ptr<Base> sp{b}). With this, it can instantiate a template (a control block) where the subclass is known.