The assumption that Hydra would remain in control past the event is based on what exactly? If they conquered the US at the END of Secret Empire then yes... obviouisly the story would bleed on past the event. But since they conquered the US at the VERY beginning, I think it was fair to assume that they would lose by the end of the story... and that's exactly what happened. No fan outrage is needed to alter what was the obvious and likely outcome in the first place.
Your entire arguement that fan outrage changed the outcome of the story is entirely based in Spencer saying Cap would win... except him saying that doesn't in any way prove this. That's my point. The fact of the matter is even if planned on Hydra winning, he wouldn't flat out spoil the ending of the event and say that. He's not going to flat out tell you how the event ends... which is exactly why you shouldn't have assumed when he said Cap would win that would be the actual outcome of the event. There's a difference between hyping an event and spoiling it.
But if Spencer had you fooled by the hype, then good for him. He did his job. If more writers did as good a job as him, events like this would probably feel less predictable.