Well, getting your eyes plucked again and again for 72 hours isn't funny, and I know that the tsukoyomi was weird made, to trick us, look that the colors aren't as before (more black than white).
it would kinda be like the one guy who is stuck getting his liver pecked out for eternity.
Yeah, The Tsuki wasn't exactly used in the normal way it seems, And it didn't seem to be used for actually causing TOO much mental pain and fatigue to sasuke. (which might be where the "He underestimated" sasuke comment came from)
Maybe it was like that because Sasuke has uchicha blood, and better sharingan control/3 tomoe sharingan, and maybe the tsukoyomi doesn't work has is full capacity with those conditions.
i doubt that, Everything that happens is under itachi's control, he most likely wanted sasuke to think it was Real, It makes sense.
But there is a slim chance your right, Which still means it was itachi's own arrogance which brought him down.
Lets say that the tsukoyomi can work perfectly no matter what, we know that Itachi didn't want to kill sasuke (don't know why, he could easily pluck Sasuke's eyes from hiscorpse, maybe Itachi is good after all? maybe there was something else?? maybe the dude with the eyes has to be alive?? who knows).
possibly he needs to be alive.. but then... what about him burning sasuke's body up to the chest?
And tsukoyomi it's a jutsu that
kills, as stated by kakashi, yes, i know that with sharingan you can make some resistance, but how would itachi know that Sasuke had that level of sharingan?? with normal sharingan genjutsu??
Itachi did the best decisions in this fight IMO
and Kisame comments that it can kill too right?
i think that Itachi' was being his normal cocky/arrogant self thinking Tsuki would be able to end it, but also taunting sasuke with the jutsu rather then fully using its abilities.
His arrogance and underestimating sasuke's skills lead to the tsuki being broken, His leg being injured, His amaterasu failing, his arm getting burned, and him forced to use Susanoo.
Because Sasuke broke out of it. Itachi sent Kakashi through 72 hours of pain because Kakashi was helpless. The same with 7 year old Sasuke. You forget that Itachi said that he can do whatever the fuck he wants to in the Tsukyomi world. If he wants it to be pink with yellow bunnies jumping around than he could do that. It's Itachi's world. Plus, there was the fact that the world DID turn into black/white before Sasuke broke out of it. So in essence your argument is pretty much baseless.
sasuke was also not bound like kakashi was, And was able to fight back while in tsuki.
besides, you didn't really disprove the fact that itachi didn't put much torture to sasuke while using Tsuki.
The fact that Tsuki can be used to kill means there is a different level of torture he can put on the people he uses it on.
he seems to have gone easy on sasuke using this one, "Underestimating sasuke's skills"