The flaw is every class but the fighter and barbarain has class features to make or bypass (via spells) higher and higher skill checks.
When the DM throws a hard or very hard check at the fighter, they have little to nothing to help them until Tier 3when they've maxxed out their combat effectiveness.
25 DC check. Let's actually look at where some of the other classes stand in heroic on very hard checks.
Unless you have proficiency and some stat or expertise in a skill everyone at level 5 always fails very hard checks.
A fighter at level 5 could easily have +5 or +6 to any chosen non-str or non-dex skill. He gets a 5% to 10% chance to pass very hard checks for those skills.
A wizard at level 5 typically needs all 3 dex, con and int. He can get a +5 or +6 to dex skills. He probably will have a +7 to some int skills. Leaving him a 5-10% chance for very hard dex checks and a 15% chance for selected int skills.
A rogue at level 5 typically will have dex and con and then much like the fighter can pick any other stat. In dex skills with expertise he can have a +10, putting him at 25% on very hard checks. In a stat he put 14-16 into he can get +9 with expertise, placing him at 15% to 20% success. Expertise in any skill without much stat bonus comes out to 0% to 10% chance of success.
No class is particularly good at very hard checks (and why is that the benchmark you chose, I have no idea). I don't think that a very hard check has ever come up in my games.
I love the six ability scores. I just think 5e implemented them poorly for the sake of simplicity. Strength could have another skill or 2 and thrown weapons could be better. Intelligence could have an innate bonus somewhere. And Dex could be taken down a peg.
That would actually make it harder for fighters to get proficiency in mental skills while still getting the athletic skills. It's like the opposite of an improvement IMO.
The Ranger was bungled. There is no spin to that.
On that we agree. But even, through level 10 the Ranger is still fine.
The fighter just includes too many ideas and it took 5 years to even imitate the biggest ones. That's a bungle in my book.
Add 2 skills to its skill list and you have something I figured out in 2018.
I have no problem with that proposed improvement. But again, it's such a minor thing that something like that surely doesn't make it a bungle.