and then you can always consider methane-fueled, propane fueled engines which have never had any tetraethyl lead in the fuel. or compression ignition engines which also never had any tetraethyl lead in the fuel.
when you think on it that way, then you will see that valve seat recession is aggravated/accelerated by other aspects of engine operation not involving a fuel additive.
in the gaseous-fueled engine, the lube oil additive package was the most influential factor in de-accelerating valve seat recession. oh, and by the way, the gaseous-fueled engine is a severe service, heavy duty application engine. your auto engine is a light duty application.
does this help you?