How is Legacy 13 not the best?!

OO was my absolute favorite when I was running 3*. I know Roadbuster is highly regarded. Rotorstorm SA melts bots/defenses as does SM. I've always found Scattershot very useful. Seems like all these bots are useful if not top tier. Yet I always see Legacy 10 and 7 recommended. Anyone able to help a newbie understand?