Beowulf is just a demon- angel- beast thing who's attacks are so wide and uncoordinated that he looks like he is just throwing his fist around, while Berial's attacks, being rare and hard to find, were at least more coordinate and took out a good some of health if you got caught in it. But, I'll give Beowulf points on being one of the few bosses that doesn't show any form of weakness and makes it a challenge to fight, despite his "Drunken Fist" fighting style. If I were to measure their strength, well... Beowulf loses in that fight. How? The King of Fire Hell vs A Guardian of Temen-Ni-Gru, I can see the difference just from their ranks. Then there is the fact that Berial is larger than Beowulf (trust me, he is), and could probably just kick him a few feet back before killing him off, or, if Beowulf were to try to get a clean hit on his head, just sweep him away with his sword. If Beowulf were to get a clean hit on his head and knock him out (I really doubt that it will be easy), he probably won't do all that much damage before getting blown away by Berial's tiny farts. Really, Beowulf is just a tiny fly that had too much drink compared to Berial, who probably crossed the border too many times (literally...).
Simply put, Beowulf was fun as a boss (the only thing that hit me was his foot) but compared to Berial, (who was at less than half of his power when I fought him, so I don't know if he grows any stronger than that) he is just a tiny fire fly.