First we are not talking about the soldiers or the common people when we talk about Garlemald, we talk about the government and their decisions. Of course a lot of the Garleans soldiers (people forced to battle by holding their family as hostages) are not bad people. But in a fight its us or them and we are shown to spare them too. So of course its better to have less fights so that less people will die. And as we are shown in Stormblood we even managed to turn some Lupins on our side thus stopping some unnessary deaths but in war this is mostly not possible.
Eorzea was not the aggressor because after taking back whats theirs (or better: Helping those people in the country take back their own countries) they did not make any moves to attack Garlemald. It was only after the summoning of Tsuyu (a plan done by the Garlean side), the take down of one of the sides in the garlean government by their own government and the news of an Ascian being in Zenos body that they acted by spreading the news of him being an Ascian in the hopes of stopping a war with Garlemald.
The talk with Varis (which they too agreed to so they have tried to do something for peace) was a failure because Varis wanted the Calamities to get his perfect race back to stop the Ascians which is something the Alliance dont stand for. There was simply no solution for peace there and I hope you did not believe that they would just surrender to Garlemald..
We also know by the cutscenes with Varis and Elidibus that Elidibus still needs the acceptance from Varis to do something. So no I dont believe that this was all alone on Elidibus. Varis could have easily just said no to such a weapon and tried to turn against Elidibus but he never truly did.
[It does not always have to be the case but if many people see things differently from you than maybe because they are right? Of course we all could be wrong either but sometimes if you are in a lot of cases in the minority then maybe its not because the others are wrong]
And I would him put more towards Zenos. Thus its in the end again just pure speculation because he is not mentioned there.