Yeah I have been worried about that too... Adding Modern has been an experiment and if they turn out "watered down" then I will get rid of them.Although I think the modern game in them would water them down a lot
The Modern hen that I use is pretty tough, and her full brother died in a natural scrap against of my wild types. So it lends me to believe they are game.
So far I don't see any issues and I'm happy with results. the crosses have dark legs and are solid white. I just wish they were taller (longer legged) like the Modern.