How about debating it using darts as the subject?
Or, literally any sport. But that's going to be difficult with someone who believes there is no luck in any sport when literally all sports at some point have luck involved. The dart hitting that little barrier that separates a high score spot vs a low score spot, it's pure luck which side the dart happens to land on. Just like golf. hitting the center of the flagstick from 100 yards away and having the ball drop in the cup vs. being a tiny fraction of a millimeter off to the side and have the ball bounce away. Pure luck.
Darts is completely a game of skill and yet luck can decide the outcome.
I can't think of any sport where luck hasn't decided an outcome. I think skill takes a person only so far. Even the very best of a particular profession will admit the role of luck. Games seem to be a little different to me though. there seems to be more games where luck plays a bigger part.
You have a better vocabulary than I do, so what word would you use to describe someone who wouldn't agree with your sentence about darts?
some COOL ones