As a landlord I think this is a terrible policy for both landlords and tenants. Most landlords have mortgages. With interest rates going through the roof, if I get to a point where the rent I can charge is frozen and it no longer covers my mortgage then I'd sell. I imagine I'd struggle to find another landlord to buy so it would be a rental property removed from the market.
It would likely also result in an increase in poorly maintained properties with landlords claiming the rent no longer covers necessary maintenance and repairs. Contrary to popular opinion, most landlords don't make huge profits from their properties, the investment is in the capital increase of the property. Once you've deducted mortgage, any management fees, and regular maintenance and repairs there is very little profit left