With a two party system you join one of them and you stand for election to be that candidate.
I'm no expert on San Francisco politics, but looking at this
https://en.wikipedia.org/wiki/2018_San_Francisco_mayoral_spe...
suggests the mayor is elected
1) From non partisan choices (Although as it's SF I suspect most will have Democrat leanings)
2) Using an instant runnoff / ranked choice or similar situation
The recent election https://en.wikipedia.org/wiki/2019_San_Francisco_mayoral_ele...
Shows that people seem happy with the current mayor
https://en.wikipedia.org/wiki/2020_San_Francisco_Board_of_Su...
Shows that the "board of supervisors" is an instant runoff too, OK not brilliant, but far better than FPTP. People don't even bother running in many situations -- district 9 for example. 16,000 votes would have won that election.
Now OK if you aren't eligible to stand for election that can be a problem, but surely you find people with similar views than you and build a campaign (if you can't find them, then your complaints really are fringe).
Complaining about politicians all being the same is easy. Doing something about it isn't terribly hard though - not at a local level, if there's really a problem. Personal 100,000 SF residents to vote for you and you're in as mayor. Persuade 20,000 and you're a council member. Of course once you have pwoer you then need to fix the problems, and that's often far harder than posting a rant online.