Traditional vaccines at least dump most of the target viral proteins into the body.
Focusing on a single protein that may mutate in the target virus has always seemed myopic to me, let alone the assumption that this approach could possibly be more effective than an immune response to the actual virus. I’m not saying that this approach couldn’t work, just that it would, by definition, trigger a subset of the immune response of a whole virus vaccine.
Edit to add: by better, I mean better at triggering an immune response. I’m not arguing against the idea that a targeted, single protein approach is or is not better at reducing illness or death and therefore shouldn’t be pursued, just about the idea that recovered individuals would be less protected than a vaccinated individual on average.