reduction in risk != rise in profit; it means safety, nothing more - nothing less.
Yes, even though it reduces the risk but it doesn't mean you can freely get the profit. Because, it just minimizes the risk like you said. It looks dumb when someone said that you can get profit without no risk, in reality that's really bullshit.
Golden rule: If it sounds too good to be true, it is.
There is no investment which is 100% risk free; and anyone who states otherwise is most likely attempting to scam.
For certain. There is no such thing as risk free in investment. It always entails risk with it. As to diversifying one's investment, it is a good thing provided that it will be invested on well researched and good coins. Although btc is a good choice, one can also choose well from altcoins. Just have careful consideration on the nature of coins to focus on.