It is not the ethanol in pump fuel causing the issues. Once the rubber lines, seals and gaskets were redesigned to be compatible with ethanol all those issues stopped.
The biggest cause of this is the lower Reid Vapor Pressure. Pump gas is blended for EFI, not a carb.
EFI is a closed system and a carb requires atmospheric pressure to function. On shut down the residual heat in the engine goes up and the fuel boils off. It has nowhere to go except out the boosters and vents. Ethanol free “clear” pump gas does the same thing and there isn’t any ethanol in that.
The other issue is the aeromatics used in “modern” pump gas. Xylene, benzene and toluene are three I can remember and they contribute to the ills we get with “modern” pump fuels.
I’m not saying to not use a return line. Im saying it’s not ethanol causing the issues.