I separate the idea into core classes and setting classes. The core game only needs a few classes to create the types of fantasy tropes that fit into all (or at least most) games. Some ideas are instrumental to certain settings, however, and should be added as part of those settings. Of course, DMs are free to allow those setting specific classes into their own games, regardless of setting.
5E did a pretty good job with it's core classes, but could still probably drop several classes. I don't see the need for the sorcerer, which is just a retread of the wizard IMO. Warlock seems like a subclass of the wizard, and barbarian should be a subclass of the fighter. The Paladin could be a subclass of cleric and the ranger a subclass of druid too. I'm personally not a fan of the monk, but at least it fits it's own niche.
Setting classes like the artificer are good concepts, but I don't like how they tried to put them into the core game later. I generally disallow the artificer because it doesn't fit into the type of Greyhawk campaigns I run. Another setting class I could see added is the Psion in Dark Sun... assuming they ever figure out how they want it to work mechanically. If they ever wanted to do an eastern setting (like when they owned the L5R IP), they might create a shugenja class, which is kind of a mix between the cleric and wizard. Not familiar with other setting's needs for classes, but you get the idea.