Everyone also should keep in mind that while Kishi may have the general layout of the manga in his head some of the fine details he adds as he goes along to fill in the gaps. The fact that Izuna's injuries lead to his death may also include the idea that the Uchiha clan was attacked or got into a conflict by some unknown element and Izuna being handicapped cause of his injuries and without his sharingan died.
I mean look at Kimimaro who was also dying of a fatal disease for some time but was still able to go into one last battle. Same with Itachi and his final showdown with Sasuke. Even though Sasuke claims he killed Itachi to the Hokages he really died of a disease but one could argue it was the battle that aggravated his condition that lead to his death.
So all this needless nitpicking over minor details here doesn't really change the major facts that have already been laid down.
- Madara was going blind as anyone who uses MS does.
- Izuna gave his eyes to Madara and later dies.
- Madara receives a peace treaty from Hashirama
- The rest of the Uchiha clan wanted the war to end
- Madara didn't trust the Senju and was angry that his brother sacrificed his life
- Madara as the leader was forced to accept Hashirama's terms cause the rest of the Uchiha clan lost the will to continue fighting
I leave it there as I want to see what details Hashirama's flashback reveals next.