It seems plausible, and I speak here as someone with no medical expertise whatsoever, that a vaccine-immunity that targets the spike protein and slows infection would still be pretty good at reducing symptoms as it would presumably slow the virus spreading inside you, giving your immune system a better chance to pick up on a specific-strain response before it's completely overwhelmed.

Given that there really does seem to be better outcomes for vaccinated people even when they have breakthrough infections, compared to completely-unvaccinated first-time-COVID-havers, there certainly seems to be something like that helping out.