You must be all flubbing kidding me.
Madara - Could not have controlled the Kyuubi during the fight with Hashirama Senju and also would never have been able to activate the rinnegan. He probably would have died or the whole Uchiha clan would just be a bunch of averange Tai and Fire-Jutsu users.
Also the Uchiha clan probably wouldnt be destroyed then. In my opinion he must be strong if he was a former of the Leaf village, but honestly .. do you really think he would be able to plant in the Hashirama DNA, survive a fight with hashi - who pwned him even with the kyuubi next to him ?
Sasuke - Ok hes really good at his chidori techniques, his taijutsu is good,too. - but hey, you miss the point. Without the Sharingan Orochimaru would have never gave him the curse mark. Also he would never ever be able to use Susanoo, Amaterasu, Genjutsu or be able to predict attacks like he did to bee with his OP swordstyle. He would've been dead too if he just walked into the five kage meeting.
Itachi - Ok, without the sharingan he wouldnt be blind, but as said he would be a averange fire jutsu user with good Taijutsu. He would not be able to use tsukuyomi or Susanoo.. Which are itachis most homing attacks. Well, as we all know itachi is also good with Weaponary, but the Sharingan helps alot with that. To be honest - I think he wouldnt even make it into akatsuki, without his sharingan.
Obito - Well, obito the star wars kid who wants to go to the dark side to revive his girl. I never had anything against Obito, but if you all think back when Obito activated his sharingan to save the half-blinded kakashi... He wouldnt have seen the guy without it. Kakashi and Obito both would be dead, but that is thinking too far. As far as we know the only reason why obito is hard to hit is his kamui. Without that he would be a pretty easy target although he might be a little fast. Still, he never would have been able to use mokuton if he didnt have the sharingan. I mean cmon .. The only reason why madara saved him was the sharingan. In my point obito would just been some regular konoha shinobi like what ? Iruka level ? - maybe a bit better. could just not think of an mid Chuunin. Oh and what I forgot to mention. Without his Sharingan Obito would NEVER be able to control the kyuubi, which means that Kushina and Minato never wouldve died. Minato would wtf pwn the non-using Kamui obito.
Now to Kakashi, the last one. - As we all know kakashi is a jounin already, he thought himself Chidori and he got his Ninja dogs. Hes also able to use shadow clones. Thats pretty much Naruto-like without high chakra. Well, tbh Kakashi still would be good without his sharingan, no doubt, but .. if he didnt die against zabuza then he would just have died against pain or in the war. He is good and intelligent, but without the sharingan, he would not have a great chance to become so uber famous Shinobi.
Now to my result.
Madara - Since he is a former nin, and we haven't seen much. (High Jounin) , (low kage)
Sasuke - (Low, to mid Jounin)
Itachi - Cuz of his knowledge a lil + (Mid Jounin)
Obito - (High Chunin if not even Mid chunin?)
Kakashi - He was a Jounin before, but I think he wouldnt have increased his Strenght much, without the sharingan. (Low to Mid Jounin)
If you dont like my opinion I would like to have reasons with cofirmed information.