Games Workshop: The Antagonist Build Problem.

As much as you like it, Abadoon is not an invincible or even Primarch level threat - in power level terms he should be around equal to the very best of the 30k Space Marines - Kharn, Sigismund, Bjorn, Typhon, Lucius etc. A level above the best of the 40k marines (Azrael, Calgar, Dante, Logan, Grimnar) but not up there with the Primarchs. He's also a bad villain if he can't be defeated at all by anyone in the setting.

Abaddon's value as a character is how he can bring the disparate Chaos warbands together against the Imperium - something the useless Daemon Primarchs seldom do. Gathering Storm gave him the biggest Chaos victory since forever so it's not like he's useless.

I find his 30k characterisation good, but his 40k characterisation overall pretty boring. He's a big boring bad guy but he's a great tactician and leader and that's his true value rather than being a combat monster. Hopefully we get to see a more interesting Abaddon now that Bobby G is back and the Daemon Primarchs are actually doing stuff. It could make for some interesting reading.

/r/40kLore Thread