I assume Kamui might be less taxing. Itachi nearly lost his sight after no more than 8 years, and in Sasukes case it was like a month. They both used Amaterasu and Tsukuyomi, Sasuke a ridiculous amount of times. Just my guess but those two probably speed up the process of going blind.
Hashi's cells dont really seem like a valid reason in this case to me. If it was simply because of that, then that does nothing to explain why it took Kakashi, a non-Uchiha, upwards of 15 years to go blind. You'd think it would be twice as fast for him, but his eye lasted double the time of Itachis. So either Obitos set of eyes are one of a kind in that regard, or its due to Kamui being less taxing on the eyes.