The alternative is to use your network directly. The very notion of "I'll publish my work and someone will notice me" is wrong. Most people in academia are too concentrated on their own work to care about yours. The only minority that cares is already in your contact list.
Not always. AFAICT my papers have often been reviewed by people I have never met and who have expertise that overlaps with, but does not fully match, mine, and I couldn't possibly contact those people out of the blue to ask for feedback, particularly because I'd never get the chance to meet them outside of peer review (they wouldn't be in the same conferences as me etc). And that's a good thing because that way I get a sort of "outsider looking in" view.
I've sure given and taken informal feedback in the past from people I know and that's great but peer review also makes the whole process more formal and less sloppy; at least sometimes and depending on the venue and to my experience.
