Never swells have over 150k miles on this same method , many sport bike racers I tend to race with when I can afford it all do the sameI dont see how your not tossing chains (oringed) with using wd40..it will swell and split the orings
Anything else tightens chains and cause friction thus slowing bike down
Grant it I do use once a week or after each long hard race
Btw my current bike has 19k stock chain always used wd40 only and still has plenty of life