I typically agree with a lot of your arguments PC, but you can't exactly put Motorola in with the "big 4". Motorola has only cracked the top 10 spot a couple of times over the past 5 years in marketshare. Samsung may have caught heat as you put it, but they've continued to dominate marketshare year in and year out, only being bested by Apple over the years. Motorola may make quality electronics and other radio equipment, but there smartphone sales have yet to crack the top 5 in the last 5 years. (Let alone top 10) so let's call a spade a spade shall we?
That being said, I do think Q4 of this year and Q1 of next we may just begin to see some improvements in this area. The fact is, your average consumer likes the TW skin that Samsung incorporates, and it continues to show year after year in sales. Your average consumer could care less about AOSP and locked bootloaders. Hell, I no longer care about it. Times they are a changing and if you don't make yourself stand out from the crowd, it'll never happen.
I believe (despite its size) the new Nexus will be the best selling Nexus ever and will change a lot of people's minds about having that true Android experience. I think it's finally Motos time to shine.... but only time will tell.
S5 tap'n