You pointed the spotlight at a bunch of insane & unstructured things... All that math you cite works great with no feats and no magic items, except almost nobody plays that way & that carefully curated balance collapses badly enough to invert linear fighter quadratic wizard. Why the heck should this particular spherical cow be praised?The idea that 5e doesn't have a structure to build on and customize on is strange to me.
The shadow of the skeleton they used to make the rules is all over the place.
I mean, go and make a class-by-class graph of gear-less characters damage output against AC 12+level/2 monsters (save +level/2) from level 1 to 20 fighting a set of 7 encounters with 2 short rests, aoes hitting 2.5 monsters, and each encounter 5 rounds long.
Then slide the length of encounters forward and back, the short rests forward and back, and look at the lines dance.
5e has piles of math under the hood.
The monsters are a combination of surprise puzzle creatures and the rest. For the rest, the DP3R, accuracy, defence and HP gives a pretty good estimation of the monster's CR, for all of people's complaining.
The system of subclasses, which has permitted 5e to keep to its core 12 (now 13) classes while allowing a huge wealth of different PC "flavors", is also pretty easy to eyeball.
The DMG optional rules? You'll note how little they change the above math. They are examples of fiddling around the clothing hanging on the skeleton of the game.
Subclasses? Neat idea sure, except every class has different levels for class/archetype gains because there are thirteen different sets of rules they use. WotC couldn't even standardize the level classes split into archetypes as more than a class by class one off rule. You only need to look as far as screwball implementations like the cavalier who waits until level seven to get their first ability related to being a cavalier rather than a odd version of compelled duel because the class/archetype scheduling was done so haphazardly & couldn't be changed without causing problems.
The system of subclasses with no entry qualifications other than N levels of Y class is only deserving of praise if the pros outweigh the cons & it's far from a slam dunk there when you start looking at problems like the cavalier's as a result of not being a class/prc of its own rather than having to fit the concept into a rather unworkable mold or things like the completely & utterly unforeseeable results of having multiple frontloaded SAD charisma based classes with multiplicative results Don't forget the fact that wotc was happy to throw math out the window so they could make a bunch of spells "intentionally overtuned" & "unbalanced on purpose" & so that they have the power of a spell 1-2 levels higher because the dead simple dmg284 table was not convenient