I think there's the possibility of taking a theory so far that the basic evidence fades until it ceases to be part of it. The engines flamed out due to lack of fuel, that fuel can only come via the supply tanks. We now seem to be jumping to a theory that the supply tanks had fuel in them that then drained back into the main tank after the crash?
So if the supply tanks had fuel in them (with this theory) why did both engines quit?
The evidence shows the xfer pumps switched off, and fuel in the main tank and none in the engine supply tanks. Certainly seems the logical way to eventually starve the engines of fuel.