50% class. 25% subclass. 25% race+background+theme+etc.
For the "race+background+theme+etc.", I actually developed an idea meant to smooth out the progression of 4e characters. Starting-character stuff got off to a very rocky start in 4e, arriving piecemeal and disjointed, things doing the same thing, things going off in wildly other directions, etc.
So I proposed the Heroic Origin.
Your Heroic Origin (to parallel your Paragon Path and Epic Destiny) tells the story of how and/or why you started adventuring. It contains everything about you except your physiology (race). Like 5e Backgrounds, developing your own, either with structured guidance or (later on) from a space of predefined, build-it-yourself components, is an intended choice, but not intended to be the primary method.
Heroic Origin provides some of your skill training, some of your ability score bonuses, and at least two meaningful features, one combat-usable, one non-combat. Your race provides the other meaningful feature, the other part of your ability score bonuses, and (potentially) limited skill benefits or the like. So, if we use this model, 50% class, 25% subclass, 15% Heroic Origin, 10% race/species/physiology.
That makes class clearly the most important element, as it should be (it is the one thing every person is completely free to choose), subclass is strong but clearly subordinate to class, and then careful selection of Heroic Origin and Species could be almost as significant as careful selection of Subclass.
I'd be willing to compromise for those who want class to be more weighty, and do something like 60% class, 20% subclass, 10% Heroic Origin, 10% species. That to me feels a little over-weighted toward class, but not to an obscene degree.
Other features, such as Feats, Spells, etc., should be budgeted separately, since everyone should get similar (if not identical) amounts of feats, and spells are a class feature shared by several classes, so their importance is already factored into the class portion (or should be).