we also see normal humans holding their own against eldar in the fluff too IIRC
. the fluff is inconsistant
The fluff is actually rather consistent on one point. If you are a hero of any faction, you can defeat a hero of any other faction even if it looks far fetch and massively improbable. After all, Space Marines have successfully dueled Hive Tyrants who are stronger, faster, bigger, smarter than them to a high degree and powerful psykers easily on par as the greatest Librarians. On paper, it doesn't make any lick of sense, but it does. I attribute this to a rather "comic book style" where in one issue a character is basically all powerful and quasi divine and the other it's defeated by Batman.