That's roughly my understanding of this as well, pulling from whatever I remember from old immunology classes. The human adaptive immune response is massively

That's roughly my understanding of this as well, pulling from whatever I remember from old immunology classes. The human adaptive immune response is massively parallel, and you can liken it to multiple progressive selection rounds for antibody candidates. As such, it is intuitive that this process would create a set of antibodies that targets not just a single antigen in multiple ways, but multiple antigens in multiple ways, resulting in more robust response (see polyclonal b-cell response) As for the latter, the issue, as already stated, is in understanding the side effects and efficacy profiles of said vaccine. Clinical trials are long and expensive processes.