Many times i've seen a Astro and one Player from his Group keeping 4 or 5 Enemies busy.
They yare jumping around like crazy because they have lots of fun knowing that you can't harm them.
Also you can see Astros storming at a Enemies Base alone. They don't care if there are 3 or 4 enemies. That's anoying because you have to fight them if you don't want to loose your Base. In the Meanwhile you can't help your group and time is ticking if they stole your Base. Why is that? Why is a class nearly invulnerable?
Honestly, if I see a Astro in the future I don't waste my time fighting them.