naruto wud just counter his chidori and saasuke wudnt see anything else cming cuz of tunnel vision. besides without sharingan he wudnt use it any way.
the moment chidori ends he can see everything again, the tunnel vision didnt stop kakashi from taking out the shadow clone, only when the enemy was completely prepared and in a better position, so that he could strike first it made a difference. and i doubt that sasuke would charge with chidori without sharingan, he doesnt need to if he has a 5 meter long chidori speer.
first of all pain never underestimated naruto becuz he had ninetailed fox in his belly. like i said sasuke cant do much without sharingan.he uses it each and every fight.it helps him fight use genjutsu see the real naruto,use chidori, and complete his battle strategies. naruto is as fast as sasuke and he is a good fighter.
pain underestimated naruto completely. if it was different, he wouldnt have fought him there, but run until god path is ready again, instead he was even surprised that chibuka tensei was broken by the fox.
naruto was as fast as sasuke when naruto was completely recovered and sasuke didnt do anything else than fighting the whole day, collapsing immediately after their fight. naruto has improved a lot, but sasuke continuously fought for like 100 of 150 mangas with his body. yes, sasuke is used to his sharingan more. but that doesnt mean that his advantages in jutsus and speed are worthless.
apart from that you cant see the real naruto with sharingan, since using shadow clone means to part your chakra into n bits, where n is the number of shadow clones. sasuke is used to not see the real one.