Why would a vaccine only be useful if it stops the spread? It's a medical treatment like any other, and we universally recognize the importance of medical treatments that reduce severe illnesses to manageable levels even when they are not themselves cures.

(And moreover, this has been true for all vaccines ever made: no vaccine guarantees 100% protection from its illness, but nearly all significantly reduce the severity of breakthrough cases.)

Edit: to emphasize: there are other ways to prevent severe illness from COVID, like monoclonal antibodies (at least, the ones that still work against Omicron). But none of them counter what you've posited (making pharma companies money), and none have as mature, reliable, and freely available of a supply as do vaccines.