Landlords are not social security. It's probably better for the city to forcefully buy them out and create a new management model of the buildings than to impose strangling limits on prices.
When you have a 3 unit building and everyone is paying less than 1/3 the market rate, it’s not worthwhile in the least for a landlord to fix up the building beyond the absolute minimum. Contractor rates have skyrocketed in SF, so even just repainting the building might cost $15k, which might represent several years of profit.
big bills (mortgages, property taxes) and bills that move [upwards] dynamically (gas, electricity, water, repairmen).
So no, I'm not assuming anything of the sort. Beyond that, landlords are extremely notorious for spending much less money on repairs than they should and saddling their tenants with the bills.