Are you familiar with the MtG mechanical colour pie -
explained here by Rosewater. From breaking down the distribution of features over classes, it feels like something similar is going on.
Each class has a role, which appears to be articulated in terms of where it gains what (e.g. in some cases the norm for a subclass is to gain a defensive feature at level x, and additional damage at level y). As noted, each class opts into one or other basic approach to combat, on a skeleton of HD, ASIs, subclassing levels, DPR steps, and spellcasting.
I'm working on a sheet to lay this out visually so that it is easy to see.