-[X][Argument] Avernus' status as a Deathworld greatly increases the amount of attrition the Orks are subject to, particularly with an idiotic Warlord in charge of it maximizing the damage they suffer; Avernus also already has an Ork Infestation from previous invasions, so the long-term effects on it are minor.
-[X][Argument] Avenues is the most difficult planet in the Tryst to take from the ground and our Void defences are considerable. With the Warbasses sheer stupidity, it's likely he'll have his Orks fighting wildlife intentionally before ever getting near our cities. However, they will get to our cities eventually. The Emperor demands we exist for war, and so we shall fight this war. But do not expect us to hold on our own forever. Not even Cadia could hold out forever, and neither can we without assistance. But no matter the difficulties, we shall fight. Avernus shall stand.
-[X][Argument] The heavily defended, underground cities of Svartalfheim reduce the effectiveness of the two main strengths of WAAAGH!!! Hedcrusha: gargants and orbital bombardment. Orks do not provoke the extreme responses from Avernus that Necrons and Chaos do, reducing one of Avernus's advantages as a battleground while subjecting Trust forces to that same threat.
-[X] Vanaheim would inflict to many casualties on our fleet, while Avernus would split the casualties some of the cities are currently expanding and wven Avernites can get war fatigued. Svartalfhiem has strong ground defenses and we can easily replace ground loses sooner and easier than fleet loses.