Generalizations that are oversimplified to the point of lacking all nuance are probably untrue because there are bound to be exceptions. Instead, try including 'many', 'most', or such as an easy remedy.

The act of landlording creates no Value. There isn't a "most" there, because it creates no Value, period.

Specifically, landlords can create value when they handle property management and maintenance (and the related costs) efficiently. It is wrong that greed has made that so rare.

Maintenance workers create Value, yes. Landlords are not creating value, here, the workers are. Landlords often pay management firms as well, cutting out all personal involvement. The minor, administrative labor does create Value, but that is incredibly small in the scope of the money expropriated from the renters.

Greed didn't make this happen, Capitalism did. The Mode of Production naturally led to this, it isn't a case of especially greedy people taking power.