There will only be strain on the lugs (without spigot/hubcentric rings) if the wheel is not centred correctly. If it is centred correctly there is no difference.
The benefit as far as I've read (I've read pretty extensively) is that the centring ring ensures the wheel is centred every time it's mounted.
The wheel is held strong when mounted correctly by the frictional force between the hub face and the wheel. The lugs are there to ensure there's adequate pressure to ensure that the friction is doing it's job. The times that people say they've snapped stud etc I would put down to basically not centring and torquing the wheel properly.
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