Potential math illiteracy aside, is this such a terrible policy? This seems to me like a nice compromise that provides some stability to the renter while still allowing the landlord to raise the rent substantially over several years.
Downsides that come to mind (but that don't seem too serious):
* It incentivizes landlords to keep empty apartments on the market longer before lowering rents to the true market price.
* It might encourage landlords to regularly raise prices more than they otherwise would, lest they forego the limited opportunity.
I'm normally much more free-market oriented, but I ask with the understanding of how much work and expense is involved in suddenly needing to find a new apartment. Just patching the holes in the drywall can take a full day. Then there's credit check fees, truck rental fees, pet fees, admin fees, move-in fees, new couch because the old one doesn't fit in the new living room fees...