...related to two things:

1) The complaint isn't that the COVID vaccine doesn't prevent ALL transmission. As you point out, nothing is 100% foolproof. Rather, it's that the COVID vaccine has very limited impact on transmission, especially over time. If it stopped, say, 95% of transmissions, then that would be a legitimate positive in its favor, but stopping, say, 5% of transmissions would mean that it is simply ineffective.

2) More importantly, it's really a question about the justification for vaccine mandates. You may be right that what's really important about evaluating the effectiveness of the vax is its effect on symptoms. That's a fair argument to make and one of the primary reasons why I got it.

But if that's the case, then there is no case to be made for mandating it. If all it really does is protect the person who gets the shot from suffering worse symptoms, then people who want that protection can get it, and the fact that other people don't get it would be irrelevant.