How much does random people reviewing other people's PRs help in practice?
As a maintainer I'd still want to review PRs myself before merging, no matter how many random people did it before me.
As a contributor, I'd hate for a random with shallow understanding of the problem/project to come in and tell me I had to change stuff or say my PR's no good, in the chance that the maintainer is easily influenced by strong internet opinions.
Drive-by contributions of all kinds suck for the most part, don't contribute if you're not going to do it properly. At some point there's got to be more than one person able to review PRs (if the project scope mandates it).
Linus Torvalds doesn't review all changes he merges, how do you become a comaintainer if not assisting with maintenance?
If you can't review, don't make a PR (or something).