Unstable Portal has a much better mean.
Bane of Doom is actually really comparable, deal 2 damage is roughly a 3/3, a random demon is roughly a random beast. But Bane of Doom doesn't require you to control a demon. That's a big difference. If you take the condition off the card and nerf it to 2/2 I'm instacrafting 2 of them, but I have played a lot of midhunter and fizzled a lot of Houndmasters.
Having no creatures alive is also a condition that inherently makes you crave RNG. If you are able to stick minions on board, you are probably winning. If you are winning, you want less RNG. Being able to hold onto a Webspinner until turn 6 without feeling obligated to use it for some board impact is another soft indication that perhaps you are winning already. (actually, in Midhunter, drawing webspinner at all is a soft indication that perhaps you are winning already, which contributes to Scavenging Hyena being not good enough for Midhunter in many cases).
Your opponent having a creature on board with 2 or less health is an indication you are probably losing, so that's a scenario you are more likely to crave RNG.
Bane of Doom offers you the ability to say "I have Knife Juggler and Imp Gang Boss in my hand, but I'm losing so badly that that's not good enough. I'm going to RNG cast Bane of Doom instead." Ram Wrangler rarely offers up the scenario "I have Ram Wrangler and Sludge Belcher in hand, and I have a Webspinner in play that my opponent left alive but I am somehow still losing, badly enough that the Sludge Belcher just isn't good enough. I am going to go for the RNG and cast Ram Wrangler instead". It might occasionally, if your opponent wiped -almost- all of your board and then dropped some really, really good threats. But not often.
A lot of people who use Bane of Doom probably don't even consider that thought process or have to, since removal spells are usually the cards you look at when you're looking anyway. The "take risks from behind" aspect is baked right into the card.