Cut all you want, complain all you want, but there once were 8 schools of magic. Transmutation already has some powers. (Red box)
So including a transmuter would be a wise move. I rather have 100 subclasses of fighter, cleric, wizard, and rogue than a runepriest, which concept is cool, but needs extra support.
Even if slayers and knights are limited fighters, most feats are usable and appropriate for all of them. So no extra support is needed and the bloat is reduced.
A bard also was a rogue once. It could have been a subclass of it too. First there were so many complains how they dared to deviate from D&D´s previous incarnations, and now there are, because they are going back to its roots.
D&D 4e is in a way going back to its roots from the beginning, but that was hidden under new shiny rules. Essentials are just doing it more obviously.
Imagine that essentials were the first books released. You would have seen less complains. When then the weapon master had been introduced, a lot of people would have complained about dailies, i guess more than now complain about the slayer and knight.
I guess in the end, it just didn´t really matter...
Why not just accept, that a game can support more than one playstyle? I did not too loudly complain about 3.5s addiditions that I didn´t like. I just didn´t use them...
(Ok, i once went to andy collins website and was very loudly complaining about the epic level book, which for me was an indicator that D&D 3.5 was made for powergamers... andy collins himself answered in a very kind manner, so even though i sometimes don´t like his design principles, he is a very fine guy.)