It may be the wrong way, but your analysis is wrong. German rent contracts and related law are such that if one very big landlord keeps rents below the "market

It may be the wrong way, but your analysis is wrong. German rent contracts and related law are such that if one very big landlord keeps rents below the "market average" that the city computes based on collected data, then the other landlords have very little ability to increase rent on existing contracts, and indirectly, the market rent then grows much more slowly than it would if that landlord set its prices as high as it could. AIUI it doesn't really matter how far below the critical number that big landlord must set rents, the key is to be below. New contracts are a different matter. This is about the typical clauses that govern rent increase on existing contracts.