The Emperor trying to consume all life in the galaxy seemed iffy to me in the first place.
I personally never quite believed it
He often disappeared for very long times
so he could have built another Empire
Everything is subject to debate as we know too little
Just thinking here, who said Arcann is only 25(ish)?
If Vitiate is Valkorion
Vitiate shared(for lack of a better word) his immortality with Lord Scourge so isn't it possible they could be older?
a lot of the councils members achievements aren't exactly mentioned directly in game
Oteg
Fleet Admiral
Jaric Kaedan
Capturing of Dread Masters
Battle of Rhen Var
Battle of Ilum
Tol Braga
Launched an attack on the Emperor
Syo Bakarn
Battle of Rhen Var
Bela Kiwiiks
Battle of Rhen Var
Gnost-Dural
Battle of Eliad
Skirmish on Bothawui
Though much of there achievements are never fully explained or mentioned
I understand your point as well