The profit from home flipping comes from asset speculation not construction. Only one of these creates net value.
There's a large grey area of old/marginal/condemned housing stock where buyers are making a tradeoff between a teardown + rebuild vs buying an old house and patching it up.
Flippers who successfully rehabilitate an old house do increase the effective supply.
Supply, supply, supply is all that matters.
100% agree that that is not what any of these ibuyer companies are/were doing.