Do you know why he holds eth in the first place? 

Maybe he is just speculating 

I don’t think many if any view alts as contenders for the best money or global reserve asset. Usually is just a bet to get more fiat or bitcoin.

Instead of trying to convince him that eth is a shitcoin, perhaps it’s better to make sure he really understand bitcoin. When he does you won’t have to tell him to drop eth, he will just know what to do.