Rem, you seem to be making my point here. Ultimately there has to be some mechanical interest. But there doesn't have to be a scripted backstory to each of these classes. I as the DM want to write that scripted backstory myself. Or I want the designers of a setting to write that backstory. I would not mind if the backstory was presented as an option next to the class. This way everyone would be happy. It would also allow the classes to be fundamentally modified by a different setting. So my argument is not that I do not want there to be a scripted backstory. I don't want it to be nailed to only one scripted backstory.
Not seeing it.
A wizard has a scripted backstory. He was taught by someone who knew magic how to cast spells from dusty tomes. He spent so much time in magical study he never learned to use weapons or wear armor. Eventually, he left his mentor and became an adventurer.
You can change "mentor" to "wizard school" if you want, but you have a scripted backstory right there. It explains how he and his textbook gained the power to blow up goblins. You can customize it with a background if you like, but in the end the core classes still spell out your origin to some degree.
Ultimately it comes down to tastes. If you only use D&D for greyhawk or forgotten realms, Having an easily accessible backstory written directly into the character class is good for you but not for everyone. For instance, if you do Ravenloft or dark sun or the myriads of other settings that people play that are not encapsulated in the scripted backstory being so far presented in the players handbook it can be frustrating.
Ravenloft in 2e had no problem with removing the paladin, bard, and druid classes in Domains of Dread. Dark Sun had absolutely no problem banning the divine power source in 4e. To make a core that would account for both require the PHB have no paladins, bards, clerics, or druids.
Really this seems like a nonissue almost, because they have provided a huge bonus to all of us in the form of backgrounds and specialties. This is an area where everyone can be happy. This is an area where they can draw upon strong scripted back stories. I would not have a problem with this. As the quintessential D&D setting is Greyhawk. Make most of the backgrounds and themes applicable to that setting. Have these presented in the PHB, along with all the Greyhawk gods and any other setting considerations.
Not this again...
Backgrounds and specialties =/= classes. You can't build a meaningful warlock using the wizard class, 3-4 skills and 5 feats.
I see fourth edition as the opposite of what your saying. It was heavily scripted. It had way too many options.
In the way fifth edition has been set up, classes should be generic and backgrounds very specific with lots of flavor. Implemented properly most people would be happy with this I think. Have your cake and eat it too.
4e told me to refluff a ranger as a rogue so I could use a shortbow.
And classes shouldn't be generic. You can buy a dozen fantasy heartbreakers with generic classes. Heck, D&D even made some for 3e. Seriously, if D&D classes are going to be so vague and generic that the terms are meaningless titles given to specific builds of generic abilities, make Next Classless and be done with it.