It depends on how big redesign we are talking about here. But if we are not talking about complete overhaul, my first objective would definitely to cull the arcane casters. So combine warlock and sorcerer into one class, (lets call it 'witch') This is a caster who has innate magic that they use intuitively, as opposed to wizards who learn their magic. With subclasses there is crazy amount of super specific bloat too. Like there doesn't need to be four different monk subclasses that all cast different spells or spell-like effects badly. Make one spellcasting monk subclass that can cast spells well and has a good selection of them, Then you can build a shadow-magic monk, blaster monk or a healy monk (or most importantly a mix of them or something else) by selecting appropriate spells. This is in general the sort of broad and flexible approach I would like to see; not every super specific concept needs to have their own bespoke set of inflexible rules when more flexible set of rules could easily cover it and much more.