You know the kicker is if the Master IS telling the truth to Gula then Gula is the traitor since only Gula deviated from his task. Ira tried to lead to the bitter end, Invi tried to mediate, and Aced was simply trying to take control as he was told he should do. Meanwhile Ava and Luxu complete their tasks completely. Gula's task however was to find the traitor and ultimately he gives up on that, he decides he won't find the traitor instead he'll find the master by summoning kingdom heart which is breaking another rule. Gula is how Kingdom Hearts is going to get involved in the war and Gula's action are what caused the unions to become obsessed with Lux collecting. If Gula hadn't done this the war wouldn't have begin and if he didn't bring kingdom hearts into it the keyblade war's devastation wouldn't of hurt the whole world. And that would be perfectly in line with the Master to make the traitor hunt themselves.
If "deviating from the task" is really the only condition to unveil the traitor then yes, although from what I gathered the Lost Page tells much more about the traitor, including but not limited to that he or she "bears the sigil".
In the last third of Back Cover though Gula basically admits that the page is written so ambigiously that he alone couldn't make enough sense of it (but the "trust no one"-mantra plus his apparent general dislike of socializing prevented him from seeking aid).
In the final update of Browser-Chi he also admits to Skuld that he tried to find the traitor but failed by following false leads.
I agree with the notion of Gula instigating the probably decisive breaking point with his beyond stupid decision to try and summon Kingdom Hearts. When I watched that scene I was innerly screaming at Ava to bonk that idiot over the head and afterwards when she and Invi talk about how Gula started hoarding Lux like crazy (and not for its intended purpose, according to Invi), I actually facepalmed as I immediately realized that this is the point where the "greedy for Light"-issue from the Legend comes in as well as the claim that the war was fought over the original KH.
We don't know the actual end of the war and the ultimate fate of the Foretellers, but we DO know that the X-blade somehow shattered in its closing stages and the true KH was swallowed by Darkness.
I think it's funny you use him using keyblades as a strike against him. Considering users of darkness have been able to commit vile acts without them fine and the keyblade is the only weapon that can defeat the darkness. The point isn't that he didn't try to stop the war; it's that he couldn't and knew as much. There is no point I arranging another war when one was already looming, it's possible he wants kingdom hearts which is only possible from the future but his motives are unknown. For him to be another Xehanort is just a waste of an excellent character.
I think you misunderstand what Hirokey is implying.
The Keyblade is stated to be a weapon crafted for conquering the Light and was originally used for evil.
Yen Sid himself states this in DDD and adds that only after the Keyblade War the few remaining Keybladers decided to use the Keyblade to "protect the light instead".
Heck, the Master himself states he didn't give them Keyblades to protect the light (without revealing what he DID give it out for).
It's also telling that "Lux collection" is only possible via Keyblade, just like Xemnas creating his artificial KH from captured hearts is only possible via slaying Heartless with a Keyblade.
Furthermore, that bangle which collects Darkness and brings the Nightmares into being has to come from somewhere too.
No one actually intends to say that he's another Xehanort incarnation here I think, but while he's somewhat ambigious it does not mean that he cannot be a bad guy.
Heck, considering his options and powers (Nomura said he crafted the Keyblades in the image of the X-blade because he knows about it) it is possible that he's actually worse than Xehanort in the end.