I didn't mean allied in the gameplay sense, but in a broad sense of being on the same side. Looking at the lore, Basium is clearly obsessed with wiping out AV/Infernals, and i agree that he wouldn't hesitate to go after a good civ, if it gets in the way.
However, what mechanism reflects this in the game? The units and worldspell are aimed at demons, but there is nothing to reflect his drive which lead him to break the Compact and really force him to go after Hyborem...
From a pure gameplay perspective, it is much better to delay the battle with the infernals and roll up most of the good civs first. Sure, you'll rob yourself out of angel reinforcements, but you'll get more than enough units during the wars and train your army at the same time.
Better have a large, well trained, SOD than a uncertain and tickling stream of fresh units.
