Apart from the other argument made that SF has a low portion of rent-controlled properties (I don't know anything about that really), your reasoning would only

Apart from the other argument made that SF has a low portion of rent-controlled properties (I don't know anything about that really), your reasoning would only work if all landlords would collude in keeping rent prices artificially high; something that is often claimed by those less informed about economics but highly improbably in reality (for a variety of reasons - there is so much literature on why large-scale collusion for price inflation of commodities is implausible that it makes little sense for me to repeat it here). Furthermore, I think you're misunderstanding pricing strategies landlords use to set rent prices. A landlord doesn't (and can't) just say 'oh I need a 4% ROI on my capital, so I need to charge 1200$ of rent for this unit to make up for the 800$ I can charge on the other'. As a landlord, you try to capture as much of the value that consumers are willing to pay for housing as you can. There are various ways of trying that, but all involve variables that are completely separate from the rental income made from other properties (somehow the gambler's fallacy comes to mind, I think both lines of reasoning are in the same class of common cognitive mishaps).