Re: Unable to buy legendary hero showcase characters? - ps4

Yes, each time you get about 8-10 vanquishes, plus 100xp per vanquish for Revenge from the grave, plus I think 50?xp for base capture vanquish.  Altogether about 200xp per dead cosmic brainz.  It can reach over 2000xp per minute.

As you mentioned, gnome bomb is a great way to get high points per minute.  I like to play GB at Sandy Sands (science/sun) to rank up all stars.