What Kakashi lost with his Sharingan:
- Sharingan/MS precognition to have enhanced top tier reflexes
- the ability to use Raikiri effectively against high level enemies
- Sharingan/MS genjutsu as powerful as Obito's
- the ability to copy and preempt ninjutsu, taijutsu and genjutsu
- the ability to warp himself to teleport from the real world in Kamui dimension and the opposite (really useful to recharge chakra or gather it and delay fights or to use surprise attacks)
- the ability to one-shot nearly every enemy he could ever face with Kamui, something that made him actually able to contend with nearly every ****ing character in the manga, no matter how strong and powerful
Now he can't even win 100 on 100 against Deidara, for example. Being faster than Sasuke as he is, Sharingan less Kakashi could probably blitz and kill him quickly; but if you make Deidara start already on his bird, how can Kakashi avoid C4? Or now he's susceptible to Sharingan genjutsu, for example, while he wasn't before.
His Sharingan in combo with his high level speed + piercing/cutting nintaijutsu as Raikiri/Raiden was pretty strong, now is no more. Before, with Kamui, he could warp anything, at least he could try. He couldn't have break Susanoo, but Kamui warps it or the user. He couldn't have break defense X or killed character Y, but Kamui let him. The Sharingan hax was something that can't be replaced in any way, especially now with power levels going to the roof. With Kamui you can go everywhere you want, warp away anything or anyone you want. You don't even need to put yourself in an harmful situation, if you have enough skill with the jutsu and enough reflexes to use it effectively. Also it was his symbol, but Kishimoto didn't care.
He had top notch reactions thanks to Sharingan, that he used to fight for more than half his life, and now he hasn't it anymore. He could use Sharingan genjutsu for offense and the Sharingan for defense, now he can't attack at that level and his defense is really not so great. He could see chakra, that could be something really helpful, and now he can't. He could copy and preempt movements and jutsu, that helped him to time his attacks and movements, and amp his jutsu pool, now he can't anymore. Had he to face a powerful defense that he couldn't have come around or break... he had Kamui. Just think how hax was Kamui space-time barrier. It required the same effort to take care to cut Gato's bodyguard's head or the 3rd Raikage's, you can warp a Doton wall and a Susanoo with the same ease. You can warp even ****ing Onmyoton. It doesn't matter how powerful your defense is, even if that could tank 10 Juubidara, Kamui would warp your ass.Had he to defend from something that he couldn't dodge or that was too powerful for Doton defenses... he had Kamui. Had he to take a rest and replenish his chakra and then launch even a surprise, unpredictable attack... he had Kamui. Now he hasn't anymore. With Kamui he had the chance to defeat nearly anyone, maybe of course he wasn't the strongest among all, of course, but he was a very skilled ninja with some of the best base abilities you can find, a wide jutsu pool and then an ultra-haxxed trump card. Now his base abilities are lower (no Sharingan reflexes, precog etc) and he hasn't that trump card anymore. I'd like to see how he could be better... de-powering him doesn't make any sense. He is of course still a S-rank/kage level shinobi, but he is not a top mother****er anymore.