My take is that from an "economics 101" perspective, a rental isn't a normal commodity.
When a vacant rental is first advertised, it is essentially "put on the market" and it's price could be determined by supply and demand in a more or less fair way (assuming "gentrification" is just demand).
But signing a lease and renewing it are very different. For the renter, leaving a rental incurs a very real cost (searching for another place, packing, moving, stress, change of habits etc). It's true that there's also a cost to the owner but it's much smaller (adverting, viewings, risk of unknown tenants etc).
So the "rational" thing for the owner to do is to try and take advantage of this by hiking up the price to include the leaving cost of the tenant. If the market is left to it's own accord, it will cause this.
Of course freezing hampers with the fluidity of the market price. A good middle ground is a predetermined max price increase agreed upon in the lease.
I think you underestimate owner costs of turnover. Risking an empty apartment for even a few weeks can erase your yield for the whole year. Landlords, then, are only likely to hike rent aggressively if it's worth that risk, in other words, when the market price is dramatically higher than the current rent rate.
When a vacant rental is first advertised, it is essentially "put on the market" and it's price could be determined by supply and demand in a more or less fair way (assuming "gentrification" is just demand).
But signing a lease and renewing it are very different. For the renter, leaving a rental incurs a very real cost (searching for another place, packing, moving, stress, change of habits etc). It's true that there's also a cost to the owner but it's much smaller (adverting, viewings, risk of unknown tenants etc).
So the "rational" thing for the owner to do is to try and take advantage of this by hiking up the price to include the leaving cost of the tenant. If the market is left to it's own accord, it will cause this.
Of course freezing hampers with the fluidity of the market price. A good middle ground is a predetermined max price increase agreed upon in the lease.