Overall whatever results in less wasted actions, within reason, is fine by me. It simply feels good to connect your attacks with a good enough ratio and a flipside it certainly feels terrible when game almost punishes you with miss streak RNG.
Positional advantage (backstab) is already an optional rule in 5e, they just need to fix it to their intended light weapons only requirement. Height advantage/disadvantage(just to remind you it's not all happiness and sunshine there) is homebrewed, but I'm totally down with it because it simply makes sense.
Neither of what you said is true unfortunately. Positional Advantage has nothing to do with weapons that have the Light property even in the *literally never used anywhere ever* optional rule of "Facing" in the DMG.
And if you think it makes sense, what is your response to the 56+ class abilities and spells that are completely invalidated by the two homebrewed systems?