I agree with your point but the main problem with phone speakers is low power and bad speakers.
My previous LG Motion 4G has a rear speaker but loud and clear, louder than Samsung S4 S5 and it does not change that much when flipped over.
My Alpha is a Exynos factory unlocked with a loud bottom firing speaker which is good , louder than AT@T qualcomm Alpha and the speaker radiates all over due to volume and fullness so side firing works.
If this had 2 speakers bottom and top edge it would rival HTC One M 8 .
So best is front facing 2nd best is side facing ( reduces bezels) and worst is back.
But Phones have been getting away with bad cheap speakers even on $600 models for a long time- starting to change now.
A speakerphone should be as loud as a person speaking in quiet to medium volume voice- very few are and HTC upped the Game.