First, this fight takes place in an abandoned warehouse according to the OP, so even though it's most likely dark and Beast is climbing everywhere, Bane completely no sold Batman, a stealth master, trying to attack him in complete darkness.
Second, I highly doubt that Bane will just let Beast pounce on him, nor that Bane has no knowledge on how to deal with opponents from above, considering Batman got taught the same things he did and hitting from above is his bread and butter.
Third, speed is equalized, so their agility is equal as well.
Fourth, according to what I've read on Eastrail 177, Beast didn't actually exist as a personality in Kevin's brain until the end of Split, prior to that only as something two of the personalities worshipped, and was, at most, a month old by the end of Glass before he was killed. Based on that age range, it seems like Beast has almost no practical fighting experience, relying on animal ferocity to win. Again, he's not stupid, but he doesn't seem like someone who is the combination of 23 intellects.
Finally, Beast won his fight because Elijah told him what Dunn's weakness was. We don't know what would have happened if David remained dry, but I'm guessing it would have been a draw.