Is this enough proof that devourer is broken?
No.
Baron Nashor can be soloed by a very large number of champions with a 4 major item build. Especially 50% defense, 50% offense builds with respectable sustain (which Volibear has in that video).
Baron can be soloed by every champion in the game with a 5~6 major item build, including the likes of Janna and Sona.
Always make a point to kill him with every champion I take for a spin in Co-Op, no champion has failed me yet out of the 100+ I've tried.
Baron Nashor is also easier to take out with Junglers seeing as he's a jungle monster and efficiently killing jungle mobs is what you tend to pick a jungler for, allowing certain junglers like Warwick and Fiddlesticks some pretty solid Baron killing pressure at very low levels with only ~2 major item builds.
On that note: Sated Devourer is a jungler item built by junglers that are doing nothing besides killing jungle mobs, of which Baron Nashor is a jungle mob. You have to figure Sated being good vs. Baron has a lot more to do with Sated catering specifically to the play-style that's good at killing jungle monsters like Baron than it does the item being broken.
I mean: if Sated was an item with a focus on AoE, front-loaded burst, CC, increased range, increased mobility, or some other boost that's completely useless vs. Baron you might have a problem. But it doesn't: nothing Sated offers is an irrelevant strength vs. Baron, as Baron primarily rewards players focusing heavily in sustained-damage and focusing on self-sustain: which is %AS champions in a nutshell.