Once again, there is no such thing as improving to hit with level. The only thing that happens is that monsters become obsolete, but your chance to hit to equal level CR creatures remain static. You level, your attack increase, but the AC from higher level monsters also increase. It's like running on a threadmill.
Only if you're fighting "level appropriate enemies" the entire game. In a more sandbox-type game, this isn't necessarily true. While that style probably isn't the style that the majority plays, it's definitely not insignificant, and I hope that the designers at least acknowledge the significance of "improving" within the context of a sandbox world (even if that means advancement is in a module).
Just because you get better with your character doesn't mean that you always have to fight demons now, because their attack and AC is equal to yours. At least, that's not the assumption my group has ever made. To my group, those improvements
are important, and the statement of "there is no such thing as improving to hit with level" is wildly off-base. I understand I may not be in the majority, but those improvements speak to the game world: if many demons are better than goblins with to-hit, AC, and hit points, and my PCs are equal those demons, then my PCs, in the game world, are better than goblins. I can now take on demons with some reliability (in a group), and take on many more goblins.
Attack bonus, AC, hit points, saves, etc. are all things that play into this dynamic. They represent fiction within the game world. And improving that is important for advancement of abilities within the game world to a sandbox game. In a more plotted game (which is great fun still) where you basically always fight enemies equal to you in power (or less, if we're using a "CR"-like system), then it's not a big deal, I agree. But that's not a universal play style. As always, play what you like
