My hair has been between shoulder and below BSL, back and forth for the last few years. No matter which length, it is much better with long layers (or sometimes even short ones when it's shorter). If not, I'm roseannadana's twin sister!
This last cut was a deva-cut with some layering throughout. It's been great! No triangle head and my 3c's are coming back!
But if your hair curls and behaves better cut straight across/one layer, then by all means do it. We all need to do what works best on *our* hair, and only we know what that is. Before and after pics would be great.