I see it as a question of whether the phb 1 - is marketably attractive... which goes beyond whether the class builds are very subtly different or distinct.
I see this essentials newbie looking at that book with un patched core rules, the same races they already have rules on how to play with, and very subtly different builds and comparing that to other books like ones with new races and brawling fighters and summoner wizards ie ... very boldly different class builds.
I see phb as plummeting almost immediately to the least likely purchase and for the most part least useful purchase for somebody who has this shiney new essentials rules.
I think the PHB will be a fairly unattractive purchase for most of the reasons you lay out -- but I think DDI will continue to be a very attractive purchase, and I think that'll prevent the older class builds and classes from vanishing.