Honestly guys, I don't know what all the fuss is about. On my 2014 CX-5 its so low and far back it is of little use as an arm rest. The elbow is nowhere near it while driving. The CX-3 has that "commander control" knob which might further compromise its positioning. I notice the 2016 CX5 armrest has a big notch out of it so the arm has room to work that commander control, and there is more room in its cockpit than in the CX3.
I would miss the small item storage it provides however, and the cup holders are so far back they will be an awkward reach.
There are always compromises in design for proper ergonomics but the I-Drive type control knob positioning was given priority as it should be. I Don't like touch screens.
Maybe the armrest was made optional because some folks might find it too intrusive when combined with the other design elements.