No evil character would side with the Absolute as it is written right now. Even the Joker, the most iconic example of Chaotic Evil out there, would be trying to get the tadpole out because if he dies to the tadpole he can't make Batman kill him instead.
Really? The tadpole gives you power. That brand + gloves = power. Evil coming to bad end is always the case. If evil characters would never follow paths that lead to bad ends there would be no evil in the Forgotten Realms. The Tav who sells her soul to Asmodius is going to end up living in hell for all eternity but she does so to get more power.
They also make those pacts because they believe they can escape them and gain more power or get a seat at the big boy table. Having a sentient being in your head that links you to the Mind Flayers and can also, when mature, obliterate your soul is leagues different. One you go to hell, with the every present idea that you can escape. The other you cease to exist, that is not worth some basic telepathy, shiny clothes and empty promises by something that you can, very easily in game, learn is more than likely a circle of Mind Flayers. Not to mention the whole absolute looks like a massive Trojan Horse mission where at the correct time and place they'll throw and switch and turn all the followers into Mind Flayers. There is also no point in dealing with the Mind Flayers as they see everything that isn't them as ants. There is nothing compelling about the Absolute from what we currently know. Now maybe, just maybe the Absolute isn't the Mind Flayer circle, but currently evidence points against.
What would you prefer to see?
Personally I like the "seductive evil" trope they've gone with. In terms of demon lovers we have Mizora who seduces a would be hero into an infernal deal and a vampire the classic archetype of seductive evil. Also, the tadpole comes to us in the form of a seducer offering us real power. We know we shouldn't but somehow we do . . .
Right away we have powerful gloves that we can only use if we take the brand. Not all evil parties will kill Gut but those who do will also have a shield and amulet.
Now you are right -- if you are going to hell anyway it only makes sense to spend damnation as pit fiend. But the fact that the absolute wants us dead should tempt us to believe that we can get an Asmodius like "deal". Perhaps we can develop that power without paying the price. That's what Sarevok thought. That's what Szass Tam thought. Both brilliant strategists whose fatal flaw was their lust for power.
I don't think good evil narrative = cost free power. I think "we know we shouldn't but we do anyway" is a) more interesting b) more in keeping with realms lore c) makes the good path come alive.