I think that's just what people with L16s tell themselves. Whether you turbo it or not, you'd be a goose not to go the extra 400cc.

In fact even moreso it's important to look at the extra 400cc as I assume this is being done on a budget = standard motor = want to minimise boost pressure.

An L16 should (very loosely) need 10psi to do what an L20B can do at 5psi.