I don’t think he is wrong... I certainly won’t be doing anything above a 10 any time soon. But with better play and gear I don’t see why it’s not possible. Especially if you have a group that understands your strengths and weaknesses and can help you out.
And if you’re running stuff over +10 right now I am pretty sure you most likely have a team you’re familiar with and communicating via voice chat. That makes all the difference in the world.