Then i suppose you don't know what a clan is.. blood doesn't = member of the clan.. There is something called being a traitor.
The "traitor" still originated from a clan, otherwise they wouldn't even have a surname. They are part of a family, lets say your brother stole your sister's money, he betrayed your family/sister but does that now mean he's not a member of the family? Of course not..
This can be applied to any "treacherous" action, even murder, the murderer would still be your brother.
Sasuke is the main antagonist.. there is nothing anyone can do about it.. its been that way since part 1 bro. Sasuke is the main guy who will keep getting in the way of Naruto's goal.. Uchiha clan provided plenty of development.. just on screen.. even random fodders who died in the shinobi wars.. provided plenty of development.. by killing enemy ninja for konoha and so on.
Sasuke is not the main antagonist unless he gains the rinnegan/hashirama's dna/the juubi. "The antagonist may also represent a major threat or obstacle to the main character by their very existence, without necessarily deliberately targeting him or her."
Madara's very existence threatens every living human being on the planet, to say that he is not the main antagonist is completely false.
Sasuke is naruto's rival, his goal is to become stronger than naruto, but now he's working as an anti-hero, wanting to change the village but his way. The very fact that sasuke has no more interest in attacking the leaf proves that he's no longer a candidate for the "main antagonist's" role.
And if you believe that is the only reason he is important to the plot.. then i don't even wanna bother arguing about this..
His death is what caused madara to spiral down the path he did. Izuna did nothing to develop any characters other than madara, he provived little significance to the story.
And no Fugaku didn't insult himself. Fugaku showed his loyalty and respect for the orders of the village heads... And if you believe he couldn't have killed Itachi with a surprise attack.. then i assume you are highly mistaken-ed.. even after knowing that Itachi was with the village.
This is an excuse, Fugaku didn't show his loyalty to the
clan, he allowed them all to get annihilated by two people for the sake of the village heads? That in & of itself is a failure so either way whether he anticipated Itachi's attack or not he failed at protecting the clan/his whole family.
Obito is my number 2 fav uchiha... but sure in hell he ain't part of the clan.
Of course he is, a clan is a family & he belongs to that family, no matter how dysfunctional he may be.