The curlier your hair is, the easier it is to get waves. It's common sense since waves are just laid down curls.
I'll speak for myself, I'm straight up negro and waves were never a problem for me. Just brush and go. Until a little later in life, I guess I was brushing my hair so much (in the shower too) that my hair became less nappy. Now I have hairs that are damn near straight. I'm still wavy but I gotta spend way more time dealing with stray hairs that literally grow straight out. These are mixed in with my regular hair. shyts bizarre.
I'm still wavy tho.
My waves just look less negro-ish and more soft. (if that makes sense). My hair is harder to maintain tho. I can't just roll out of bed. I have to lay my shyt down for at least 30 minutes or it looks crazy. Also, its easy as hell for me to sweat out my waves... if that makes sense.