So you just want less stuff gained at each level? Depending on the class, as well as whether or not you multiclass, some don't necessarily gain much at each level. Also, if you did that you'd have to scale back difficulty some, as the game assumes that you have a certain level of abilities by...
While 5e doesn't have 30 levels they still give players options for play at 20th level and allowing characters to keep improving beyond what you get at level up by allowing ASIs to be taken, with a higher cap, gaining boons, and feats. It may not be the same as just continuing to level up, it's...