Look at the data from the UK. The pandemic is far from over there, although hospitalisations are far far lower than previous peaks. There is a non-significant amount of immunocompromised people in the UK (1million+). Maybe the data we are seeing is because the immunocompromised people who take risks all ended up in hospital and died.
Maybe, what you are left with is a huge number of people scared shitless at home, hiding, lonely, scared in a country where everyone is being told everything is fine. My father is in this position, double vaccinated and tested negative for antibodies. Current data shows extremely low efficacy and antibody production in immunocompromised people.
Yes, but the fact that symptoms tend to be much weaker in the vaccinated likely means it's less likely to spread from them. Currently, the problem is that we have those breakthrough cases, plus also the unvaccinated still spreading the disease.
That said, it's true that the new delta variant may mean we need further boosters.