market power means you can capture all of the benefit for yourself - e.g. you charge what the market will bear for a service rather than what it costs you to provide that service.
So you cannot argue that you will make a unit more valuable, thus increasing demand for the unit, but that a landlord who has market power will not be able to raise prices to fully capture that benefit.
Rent control is such a benefit that makes a unit more valuable, and landlords are able to charge more, fully capturing the benefit to the average renter.
This means long term renters underpay, short term renters overpay, the landlord does not pay any more, on average, given the mix of short and long term tenants, but the short term tenants subsidize the long term tenants.
So all of these plans to pass laws preventing or obligating landlords in some way will always result in higher rents to fully push the value of that benefit onto tenants, assuming that landlords have market power, which is a safe assumption in constrained areas like San Francisco.