[GAMEPLAY] Darius Full AD doing 1.6-1.8k damage level 3 ult?!

Recently, I heard a friend of mine complaining over a VOIP program that Darius was overpowered as of the very moment that patch 5.4 came out. Checking over the patch notes, and every patch since 5.0, I couldn't find anything about Darius getting super buffed. Now either this is just something that everyone figured out, or else something was glitching. So I entered a game and had him as Darius, by himself, on the enemy team vs me and 4 beginner's bots, did the test as Mundo, fed him 30+ kills early to get things over with, and then proceeded to get myself to full build Mundo. After hitting my ult and standing there, with three IE's, a Blood Thirster, a ravenous hydra, and boots, he was able to burst me 100 to 0 with just pull, Q, auto, E, auto, ult. Mundo was equipped with (obviously) warmoggs, spirit visage, SFC, frozen mallet, thorn mail, and randuins, with over 4.5k health at max. His combo did over 6k damage, without full stacks. Now, given what things like Mobafire say about Darius' scaling currently, that shouldn't be possible under any circumstances, like literally no matter what. Am I missing something here, or is this just the way of the Darius? Because apparently, his play style changed significantly after patch 5.4 came out.