I think we differ in how we define organizing. I see it as the ability to effectively organize large groups of people, logistics, supplies, or military responses. I would not consider 'Out backstabbing the backstabbers' as under the label 'organizing', that's more of a tactics thing. I also don't think anarchists should participate in backstabbing at all, as that reduces trust in the whole effort, IMHO, and it doesn't seem likely that a large anarchist collective would agree via consensus to do such a thing.

Anarchists in 1918 didn't automatically assume their anti-capitalist allies would betray them in that manner, it was up to that point unprecedented in history (though predicted by Mikhail Bakunin). Anarchists the world over supported the Russian revolution until they visited the USSR (such as Emma Goldman) and it became apparent that it was becoming a new state dictatorship. This was a learning event that showed MLs cannot be trusted despite their appeals of leftist unity.

The Anarchists were fully aware of this betrayal by 1936 in Catalonia, but the circumstances were dire enough to begrudgingly ally with them once more, as the USSR was the only country in the world with the already existing productive capacity and willingness to supply the revolution with needed logistics and heavier weaponry such as tanks and artillery.

It was no fault of Anarchist organizing that those logistics were needed, it was just circumstance that Catalonia did not have any tank manufacturing set up before-hand (something that can take years to do), and that their enemy was stronger than it normally would've been at that point in time.

There is nothing they realistically could've done to 'out organize' the MLs, as organization was not the issue. The issue is that the MLs were an enemy, but they were the enemy of another enemy (the fascists), and the lack of logistical help from the outside world left them with the options of trying to fight both enemies at once, or hope that they can first defeat the fascists before needing to defend against the inevitable ML betrayal. The fact that the MLs ultimately chose to betray mid-fight with the fascists was likely pretty unexpected, since it didn't really make sense for them to do so in that moment in time (since it made the MLs lose too).

Thanks to those events, we know now it's probably best to never ally with ML's under almost any circumstances, even dire ones, and going forward we can avoid those mistakes.