The GM confirms that he did make a mistake.
Now, on the one hand, me not sabotaging the mission would have meant a different game.
On the other hand, it's not as if something happened that was against the rules, it was simply not my intention. The game would have gone 95% the same if I had chosen to sabotage.
Either way, it doesn't change the actual state of the game which is, indeed, won by us Spies as correctly analysed by Panzer.
Now, as for what we can learn:
1) Really, really, really stop accepting teams so easily. After a failed mission, the first proposal goes through? Really?
2) There's nothing wrong with Strong Leader. Yes, it won us the game, but because of a combination of coincidences. Make one change on the leader order and it doesn't guarantee us the win. If just a single extra proposal had been made earlier, it wouldn't have guaranteed us the win...
3) What I do feel we should do is make these landslides less likely. One officially endorsed rule variant that we've never tried is to allow the first Leader of a mission to decide what mission is actually attempted, ie. how many people need to be sent and how many sabotages are needed. I'm not sure we should go all the way, but I do feel that being able to take the 'requires-two-sabotages' mission once you're donw 2-0 allows the Resistance a better fighting chance.