Regardless of if you like the implementation or not, the bottom line is, that isn't an excuse for poorly making use of phone real estate.
So in the name of symmetry we poorly make use of phone real estate? Wouldn't it make more sense to have better engineering instead?
So is it your assertion that capacitive buttons don't take up any space at all? Because in order for what you say to be true, they would have to have no space requirement at all. The bottom line is, Samsung managed to include these things, and still use less bezel.
Well, I admittedly don't own a Nexus 6 (yet, it's on my Christmas wish list) so I cannot perform exact measurements, nor compare the 2 devices side-by-side but a simple visual comparison of photos of the two devices shows that the portion of the display dedicated to the soft keys and remaining bottom bezel appear to take up roughly the same amount of space as the bottom bezel on the iPhone 6+, a bezel with about a mm of clearance on either side of that fingerprint scanner. So yeah, it apparently does take up the same amount of space.
I could use your exact statement against you, as it relates to Apple not efficiently using their phone's real estate. So with that said....You're also not an engineer at Apple with an intimate understanding of what's required to make the device function at its best, nor offering any viable solutions to your perceive problem with the device. So unless you can prove my last statement inaccurate, how about you keep the smartphone design and engineering to people who have a clue.