The Body Flicker, the Shunshin, is literally one of the most ridiculously common techniques in the entire series. If you're saying one of Shisui's MS powers was that, he would have really lost the lottery on MS abilities. The reason techniques like the FTG and Kamui are so threatening is because they aren't merely enhancing the natural movement speed of the user (the function of Shunshin), rather they actively warp the caster through space and time.
Also, it's probably worth considering that both of Shisui's eyes cast the same technique (Koko-amatsukami), so they are likely both only capable of that technique. We're seeing the same thing with Obito's eyes; both only use Kamui. Other than that I haven't been paying much attention so I'm not entirely sure what you're arguing.
I am a leaf on the wind. Watch how I soar.