That supposition was questionable last spring and summer, and now flat out wrong with the current delta variant. It is hitting young people considerably harder than the previous variants.
I've been practicing medicine for more than 15 years, and I have never in my life seen so many young, otherwise healthy people wiped out by COVID-19. Fortunately, I don't have any patients in the 20-40 year old bracket who have died from the disease (although at least one passed it to a parent, who then died), but more than a few required hospitalization, and none of those who were unlucky enough to develop PASC (aka, "long COVID") have yet to recover to their previous level of functioning. Even almost a year later.
The standard vaccine schedule includes many diseases with far less severe and far less frequent complications than COVID-19. Yet, nobody but an antivaxxer would say, "That's OK, go ahead and skip your MMR. You probably won't get the encephalitis from measles, infertility from mumps, and who cares if your fetus gets birth defects from rubella?"