I was also going to mention the episode order. But going from the rough translation from Japanese, isn't the real title "The Greatest Robot on Earth"? Since Atlas didn't live on Earth most of the time and as a result didn't belong to any country, perhaps he wouldn't have mattered to the sultan. Many years ago, somebody else pointed out that the story seemed to represent a war between countries, perhaps even for oil.
I think Atlas would have won easily against Bruton because Bruton lacked mobility, not being able to fly very effectively. I think it left him vulnerable. If Atlas could defeat a bunch of aliens, he could have defeated him. Of course, then he should also have been able to defeat Astro; I don't know if this was a conscious choice or not, but it's as if he couldn't make himself destroy his brother, or at least not destroy him using powers that were not within himself, such as using the crystal castle or another mean.
I don't know who would have won between Bora and Atlas. We didn't get to see a lot from Bora. I haven't read the manga so I don't know if the fight ends the same way, but I have always wanted to ask Abra (?) how he could seem to be so sure that Astro would defeat Bora. It seems to me that Astro was a little lucky there!
BTW, Bruton's mean to fly is so weird.

I've always wanted to know how he looked inside, surely he was at risk of having a few wires getting tangled.
