The Recapture of north-east Beleriand

[Macalaure]

I see your point, but I didn't mention it because it is not affected by whether Maedhros recaptured his March or not.
However, it seems to me, that Tolkien estimated his fault quite high. Only after he tried his strength did Morgoth send out his spies. The Easterlings that already served him must have told him before, but for some reason their early reports didn't seem to bother him.

Anyway the treachery of Ulfang and his people was the deciding factor of the battle and without it, Morgoth had not won the battle.

I'm not so sure about this. Morgoth was strong, and maybe would have won even without their help.

But that is an interesting topic as well:
What were the factors of the great defeat?
What problems could have been absorbed by the Union, which were decisive.

I think the main factor was, again, our beloved Oath...
Without it, no misdeeds of Celegorm and Curufin in Nargothrond
Without their misdeeds, Nargothrond maybe (if Finrod was still alive: definitely) would have joined.
Without the oath, there would have been no haughty words towards Thingol, and maybe even he would have joined.
With all available forces united, I'm quite optimistic.