Whilst I'm not a dominant, (although some people might disagree lol) I hope you don't mind if I state my pov.

Like with everything else in this lifestyle, you do what works for you. Many dominants came to their roles after being submissives. In my opinion, that might make them better Dom/mes in the sense that they have experienced the other side of the spectrum. The keyword is "might."

However, there are plenty of dominants, who couldn't even imagine taking on the role of submissive. Doesn't make them bad.

A good Dominant, as far as I'm concerned, has an avarice for learning what can make him/her a better Dominant.

There are many Dom/mes, too, that would not try something on their subs before experimenting with themselves first.

So, to answer your question, your friend isn't necessarily correct. There is nothing written in stone as to what does or does not make a good Dom/me, except for the desire to want to be a good Dom/me

P.S. You might wanna have this moved to the "Dominant's Dungeon."