You can check polish and care for quality. There are some significant examples where in the 2014 PHB there was a lack of care and attention paid to actually doing what they were trying to with the class.
In 2024 every single one of these has been patched if not outright fixed (a few were by Xanathar's and many by Tasha's).
- The 2014 Beastmaster Ranger is, oddly enough, not an example of this; instead it's an example of missing the class fantasy and arguably psychotic design. The 2014 beastmaster is balanced ... if you consider your pets to be disposable and throw them into combat without trying to keep them alive.
- The 2014 Warlock is my favourite class in the game. But what is actually put in the PHB was clearly just thrown together with no love and no polish; a full quarter of the invocations just add a spell known to the warlock list (and there are other bad ones), many of the others are bad (there are a few lovely ones in there), and iconic warlock exclusive spells like Hunger of Hadar don't scale with spell slots. And then there's the Pact of the Blade. The 2014 Warlock clearly isn't the class it could be.
- The 2014 sorcerer is a wannabe wizard who knows too few spells - and other than twin spell the metamagic isn't all that and the numbers are very small
- The 2014 monk ... what do I need to say?
- The 2014 barbarian basically stops at level 6 and the 2014 fighter at level 11
But the thing is that the macro level design goals of the 2014 rules, removing the pain points, were pretty good. It set out for and succeeded at mass market appeal and getting in the way the least of any edition. Although the implementation is frequently lacking the structural basics of removing all the pain points and having a very good Tier 1 experience and pretty good Tier 2 worked well.
There is always room for improvement and we should never let perfection get in the way of good enough. Which is all I've been trying to say. I'm not saying that 5E is the tightest, best written TTRPG ever written because that's an impossible standard with no way of being measured. Some people might look at a one page TTRPG like Honey Heist and say that it meets those measurements better because it has no fundamental flaws. It's obviously not very in depth either of course.
I just reject that it's been successful in spite of the rules or that the game is successful for reasons other than that for a lot of people it just works for what they want out of the game.