Well, the Lodge is destroyed either way, whether Council is created, or not. It is not like either council and no Lodge, or no council, and the Lodge.
Exactly, that's why Emhyr's plot succeeded regardless whether the council is created or not.
The Lodge is a leader for mages, them having their own agenda (part of it being mage empowerment) is irrelevant. They were at least capable of organizing mages under one direction (they instigated the creation of this council), as opposed to the Council that was split 3 ways.
The council in TW2 would have been a major problem for the empire if it was the Lodge controlling it. Eliminating the Lodge or weakening it would reduce the threat of mages significantly.
It was Northern mages who won the first war, and with ease. The Lodge did not even exist.
That's why I said "future members." Philippa Eilhart was practically the leader of the mages at the battle (of which there was 22, 14 said to be killed so it was not with ease).
Emhyr sent this mission not for kicks, and even Henselt's assassination wasn't a priority. The entire deal was about not allowing the Council and the Conclave to be created.
No the entire deal was to eliminate the Lodge and weaken the North. The Council is a bonus. Even Letho says it "lay blame on the sorceresses." In fact the whole affair in Loc Muinne with Letho showing up, was improvised by him.
However difficult it was for Nilfgaard to pull the Thanedd coup, doesn't change the fact that it was split 3 ways before that. One side was going to join them, the other was going to stay away. So even if they didn't pull the coup, the mages would likely not have been a decisive factor in the 2nd war (which was a more serious attempt than the first one, as Emhyr had fulfilled his objective).
The Lodge, an organized cell of mages, is more dangerous to the Empire (esp if they control the council as they intended and as Emhyr sought to avoid) than a divisive band of mages that can be swayed either way, esp with someone like Radovid alienating them as the epilogue said.