Some of London's Underground lines do share track along some of their length, like BART, but overall this is an exception rather than a rule, e.g. some of the D

Some of London's Underground lines do share track along some of their length, like BART, but overall this is an exception rather than a rule, e.g. some of the District and Circle overlap, and indeed the Metropolitan also shares with the Circle. And I agree that for the purpose of a trip within this core, you'd only care about that 5 minute wait, which is pretty reasonable, much as often passengers won't care if this is a District Line train or a Circle, since the stop they're going to is served by both.