If you don't like "Stevie", don't call your kid "Stevie". Pretty simple. I'm a man, almost 50 years old, and my friends call me "Stevie". I don't take it as diminutive; I take it as a term of affection. I am proud to be called "Stevie".
Sorry, but "Stevie" is not a strong masculine name. It's not even close to that. It's definitely unisex, but more feminine than masculine in my opinion.