I'm completely with you. I'm actually slowly planning my next campaign (my turn in the DM seat isn't until 2018, fortunately), with the following changes:
1) All new set of base classes, all of which are 5 levels long.
2) A whole set of "prestige classes" associated with magic items, where the prestige class levels strengthen the character's ability to use the magic item, and also give them some intrinsic abilities associated with the magic item. Basically, turning class levels into a form of treasure. Finding a wand of fireballs gives the character access to a 3-level prestige class that grants fire resistance, additional charges per day of the wand, and additional spell casting. The ghul lord's tome gives access to animate dead, the necromancer ability to create stronger undead, and some other undead themed abilities.
3) Multiclassing will either be not allowed, or only allowed once. (Still working on this). Characters won't be able to pass a certain level (5 or 10, probably) unless they gain access to prestige classes.
4) The campaign is set in Al-Qadim, so the base classes will be built around those tropes, and roll together background and class concepts.
I'm aiming to turn the expectation of higher level abilities away from the assumption that just earning XP will grant them. If you want to be a powerful caster, you need to seek out tomes and wands to learn higher-level spells. A warrior has to find magic weapons or hidden experts to learn new abilities.
Basically, I'm trying to turn 5e into the OSR/MOBA/Talisman hybrid I've been tinkering with for the last couple of years.