Again they are not the same nor close to being the same. They have 1 thing in common, and they work differently in how they can achieve things. Lee never stated that about Neji and none of them cheap tricks ever worked. Ill explain.
Byakugan Allows you to sense and detect 360 Accurately basically, So no matter what happens or what you do they will know it before and the moment you Shunshin or do anything. They have 2 ways of stopping all speed users that uses Body flicker and even the Pure Taijutsu users who use Taijutsu to allow Speed (Lee and Guy do not use Shunshin).
Just in case you didn't know the definition. And you even agreed They would be able to see and track Itachi so ima move on to the next point.
Then you compared the rinnegan to byakugan as if they are even close to working the same. lmmfao Really? Please leave the Rinnegan out of this, thanks!
Sharingan Works differently in the sense that they predict what you might/would do in front and front only! Once you leave there vision they have to then try to lock on to you once again and predict what you might do next. As seen with Kakashi and Zabuza, kakashi and Kakuzu, Sasuke and Naruto VOTE, sasuke and itachi, sasuke and killer bee etc etc etc.
Byakugan senses everything accurately 360! As in no matter where you might appear they have you tracked no diff! Unless you shrink to the size of a vertebrate about nickle size btw. They also detect everything the moment it happens no diff! So with that There abilities shine bright!
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Right before any attack lands! No matter how fast you think you might be they will always beat you since it takes Zero time to omit Chakra from ones body. Itachi does not have any attack or punch that will even make them smile! His shunshin will be useless since they would know chakra to feet equals trying to blitz and with there Vision whether behind or in front they can counter itachi with out even blinking!
Then we have the ability to see everything in a Freeze frame:
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With this effect and ability they see time as if it has stopped (that is how fast there eyes are working if you don't understand), Then having the ability to alter anything they please with pure chakra alone that is instant! Itachi will not only have all his attacks blocked no diff, he want be able to predict it either. A full body Blow will kill him or badly injure if to close as well.
Then you bring up Lee in gates as if Itachi has that Taijutsu Speed (he doesn't, shunshin isn't taijutsu if you didn't know). And Nor can Itachi hit even close to 1/16 the power lee possessed nor spam the speed lee spammed appearing almost instantly in multiple locations. And I guess lets ignore the fact Neji was keeping up and seeing everything lee was doing, and was surprised Lee had that ability; he wasn't scared or "shitting bricks". It was more so Surprised Lee had such a secret. Not once did he comment on "Too fast" or "too powerful" or "I cannot see anything" etc etc. SO please leave that alone unless you have words on kishi/manga stating this? Add Neji always held back as well since they were friends and teammates! Why would they fight to kill again???? Mute point.
Byakugan isnt rinnegan nor sharingan. Nor do any of them users (bar Nagato ST, or using Susanoo) have the ability to defend themselves instantly! Unless you can show an sharingan user No susanoo having a better def then Omitting Chakra instantly from there body??? Can either eyes do this:
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Hit 64 times and move there body in conjunction in mere seconds? There eyes and body is adapt to fast movement it isn't even funny. To preform 64 Divinity you have to have the eyes to be able to react instantly since each hit is precise and pinpoint with perfect detail one after another and would need the body to move your arms and torso with your arms and hands and feet moving in such a high speed to the point you see literally nothing but one motion hitting them multiple times! Itachi has never shown anything on that level of speed, using a few handseals fast is childsplay, Throwing kunais that you can see and see his arm moving is also childsplay. When 64 divinity is in play you see nothing but after hits after he has counted (4, 8, 16, 32, 64). Only Gai has shown anything close to this ability, and he needed 6 gates to achieve it.
Please stop using the outdated Databook! please! Unless you are saying Kurenai is equal to itachi in genjutsu? Or Gai and kisame is equal to Tsunade in strength? etc etc I can keep going on how flawed that out dated thing is it isnt even funny! The fact that you are relying on it speaks volumes...
And just in case you still do not get it. It takes no time to omit chakra from there body, they do not have to move a muscle! That is why you cannot compare them to the other eyes since they have to move to react or block any attack that might happen. Learn the difference please! And detect and sense everything accurately and see anything chakra related before it happens>Body prediction. Since sharinagn has to read and predict is the reason they cannot react to speed demons with out having o use Susanoo (Sasuke vs Aye prime example). Hyuga's have chakra as there def and means to alter attacks and counter attack. Show a 3 tomoe user using chakra from there entire body then we can compare the eyes... I'll wait.. His basic Ninjutsu usless, taijutsu useless, speed useless, genjutsu useless. What is next itachi is god as usual?