For all my wariness of whats coming out of pf2, i like the idea of "class feats". In my mind, a 5e advanced phb would take the chassis of existing classes, and exchange asi/feat levels as well as class ability levels, and let them choose from a range of tiered feats (and they could also choose general feats at the asi level).
5e does this to some extents, such as battle master fighter or totem barbarian, but i think theres more room.
For example, a beserker barbarian could choose if they want to gain immunity to fear, gain an ability to create fear in combat, expertise in intimidation, extra speed, being able to maximise damage once per short rest, upping rage damage, adding a charge maneuver, etc
These are off the top of my head examples, not tested, but can serve to show that a party could have 2 beserker barbarians that are quite different. Perhaps one is an expert in intimdating and creating fesr amongst enemies while being immune to it themselves, while the other charges into battle and causes maximum damage.