[RedDevil]

The bypass will most likely end up where the radiator return feed is, so indeed for the engine there is no gain in my concept.
But there is a benefit for the radiator.

The heat exchanger (heat 'mixer' would be a better description) makes the engine receive warmer water from the radiator; as a result the engine temp would rise so the thermostat will send more coolant to the radiator instead of the bypass circuit.

So heat exchanging will increase flow through the radiator.
It will also bring down the temperature of the water flowing into the radiator, so that heats up more evenly.
These effects both reduce thermal stress on the rad.

It will also prevent the buildup of pressure before the whole radiator is hot; even if the water leaving the engine is above boiling temperature, the drop from the exchanger will bring it down unless the reflux is boiling hot too.

In short; this would solve the uneven heating of the rad under low load but retain full capacity when needed.

This is not a substitute for active grill blocking, but could be a useful addition.
It will definitely make the system less critical to which method is chosen to switch the block.