Mainly this idea that the prediction capability of the Uchiha is one and the same with the Byakugan's visual x-ray.
No, they are not one in the same.
X-ray vision is a base ability of the Byakugan.
Predictive capabilities are, by definition, not a base ability of the Sharingan. Now stick with me on this one before you yell my head off as to why I'm wrong.
I'm using the word basic with the definitive sense that it's
Something which cannot be broken down further.
It's two different mechanics as the Sharingan's trick involves remarkable memorization and recognition on top of just being able to view the muscles of the enemy.
Going by your own words, the Sharingan's abilities are a byproduct of Muscle memory, visual prowess, and recognition. In this sense, it is not a basic ability, but rather a complex one, meaning that it is created of many smaller abilities.
So we've got three
basic abilities namely: visual prowess, memorization, and recognition; that come together to form a complex ability- Prediction.
We can all agree that in terms of the
basic ability visual prowess, the Byakugan is superior. For the intents of this argument, we don't even need to call it superior, we just need to agree that the basic ability exists.
The Byakugan functions rather differently; as it focuses on spotting chakra networks and greater peripheral vision and enhanced perception speed. Nothing about being able to memorize those movements to a degree of prediction.
We can agree on this, the instantaneous combination of recognition and memorization are what I call auto-pilot, and the Byakugan indeed does not have that.
However, the structure and musculature of the human body are set in stone, they're not going to change. For a given action, e.g. punching, the same general set of muscles, ligaments, and tendons will move regardless of who performs the action.
Given that
Prediction is really three basic abilities, what the Byakugan lacks are memorization and recognition.
But then again we don't need the Byakugan for that, the Human Brain is more than capable of performing memorization and recognition. Through the observation of the same repetitive process over time, the brain would no doubt grow capable of both memorizing this process and recognizing it should the same process be placed before it in the future.
I'm calling that acclimatization until one can recognize and recall an observable process- Training.
Tweaking something to basically give you the exact same power as another Kekkei Genkai to me is fundamentally changing something; even with a "reasonable" base. It makes the unique traits of what should be a bloodline ability questionable and it cheapens the Byakugan by making it "compete" with a Sharingan by copying one of its tricks.
Except by my logic I've tweaked nothing; what the Byakugan lacked was made up for by the existence of a Brain -a processing supercomputer (and that's without boosts by mythical energies like chakra)- and hard work, to achieve the same results.
Predictive Abilities aren't Unique to the Sharingan, regular human fighters can predict their opponents through sheer experience and recognition of body language. What's unique to the Sharingan is the
instantaneous achievement of this feat without the need for training.
It does not make the 'unique' trait questionable since the trait was never unique, to begin with. To give an example, Uchiha w/ Sharingan are born as Black belts. Does this mean that black belts are unique to the Uchiha? No, what's unique to them is their ability to bypass the lower levels of training.
It does not cheapen the Byakugan because I've done nothing to the Byakugan, it remains with the same basic abilities it's always had. It's not being upgraded to 'compete' with the Sharingan by copying a trick, because this trick is, in fact, no trick at all but just a shortcut to achieve a result.
The Uchiha are taking an Uchiha-Only shortcut (the Sharingan) to the finish line (Prediction). However, my point is that it's not a race in which only Uchiha can run. They might certainly get to the goal first, but that doesn't stop others from making it there through the long route.
Even a regular human without special eyeballs could develop predictive capabilities by gaining the experience to read body language because this accounts for the Recognition and Memorization aspects of this ability. It wouldn't be as strong as a wielder of Dojutsu's because they'd lack the visual acuity, but memorization and recognition aren't an issue.