IMO, the main issue that is being 'missed' by some here, is the fact that lambda=1 closed loop control is only being used at light throttle, light load operating conditions, to enable the closed-loop lambda control mechanism in the ECU to overcome the lack of injector duration resolution at light loads creating unneccesarily rich or erratic fuelling - this gives the opportunity to get good fuel economy and emmissions FOR FREE, with no downside. Once load or rpm rises it releases the closed loop control and reverts to open-loop base mapping at a suitably rich setting for the conditions.
You can run at lambda=1 or indeed quite a chunk leaner at light loads all day long, without any fear of creating any overheating... it's got absolutely nothing to do with the melting potential of a high-output engine under boost conditions, or the benefits of adding some fuel under those high load conditions to cool things down a bit, which everyone agrees on...