Which is, IMO, an issue mainly because your max skill ranks are tied to your level which is in turn tied to everything else. It's an inherent flaw to a class/level system that tries to cleanly integrate skills for everyday tasks and pigeonhole the world into classes. You don't run into the same issues with a completely skill-based system or with a class-based system that doesn't have sharply defined and limited skills.
What you see as an "issue" I see as a compelling ludonarrative. It's a world of adventure. Farming your fields means killing goblins. Being Einstein means fighting off mind flayers. That's
awesome. That's why professional adventurers are required.
I get that not everyone wants that kind of world, and that even if you do you can make it without NPC classes, so I'm not married to the mechanic. But I don't think it was silly.
Personally, I think the 0-level system combined with reasonable DM assumptions is dandy, and there's not much daylight between that and Level 1 NPCs with reasonable skills running around.
Reasonable DM assumptions is certainly the easy way out! Fortunately, I bet bounded accuracy helps make that a reality -- and easy to implement -- in 5e.
It's fine if you want to use "you must adventure" as a baseline for a world. But it's not ... um ... versimilitudinous.
I think there's an important distinction to make between "realism" and "like the real world."
"Getting better requires adventure!" isn't very much like the real world. Getting better in the real world requires hours and hours of endless tedium and repetition. Which wouldn't be very fun in a game.
But if you make a small willing suspension of disbelief for the purposes of playing an engaging RPG, and are willing to entertain the idea that in this world, you can't get better by repetition, and you only get better by risking your life...
You can base a consistent, logical, not-insane world on that foundation. If getting better at anything requires risking your life, as you get better at studying obscure works of art in a D&D world, you get better at a whole host of things alongside that, which are useful in generally violent life-threatening situations.
In a D&D world where you're a 1st level commoner and Einstein is a 20th level expert, Einstein isn't just smarter than you, he's also a hero who has faced death in pursuit of knowledge. Einstein could kick your butt. And he's super-wealthy, too. And his INT isn't just slightly bigger than average, it is like unto prescience.
That's appealing to me. But it certaily doesn't fit with certain styles of game, and it doesn't require NPC levels to do.