The battle between the two Beyodners was rare; that was something that everyone present within the Imperial Defense Forces could steadily agree on because it was indeed the truth. Or, more precisely, battles between Beyonders in places like the Alaric Star Domain were rare...
Among the hundreds of millions of Star Systems that were creating the Andromeda Galaxy, not many of them could say that they were able to host the fight between Beyonders on the level of the Elder Brain or the Grandmaster Arsit Byrmellir.
When Beyonders fought, they would usually fight in the Cosmos, between the galaxies, because their fight could easily destroy large parts of the galaxy; this was especially true for the top-sequence Beyonders with very destructive Psyker Abilities.
When the Beyonders were fighting in any inhabited Galaxy, they needed to control their power strictly and with the utmost precision and care, or else they would destroy everything around them in a few breaths.