There is simply no 'one good solution' for difficulty that fits all games. You cant point to "Well 'x' game did this, and so every game should do that" because it just doesn't work like that.
Main thing I hate is when harder difficulty options are locked behind completing the game first. And even then there's exceptions where I think it can be ok like in Ninja Gaiden Black or something where a lot more effort gets put into these higher difficulties and are very clearly built for people who have already mastered the previous level of difficulty and not something anybody could just jump into for their first playthrough.
I also really appreciate this slowly cottoning trend of games offering custom difficulty settings rather than strict 'Easy, Medium, Hard' presets or whatever. It's hard to know what custom settings to choose when first starting out, but usually a bit of time in the game allows you to get a sense of things and then calibrate the difficulty options to your liking.
I don't think that's fair. As stated already, you can't game balance for any specific target - all players have different abilities. Devs could only pick something that seemed right, likely didn't have much by way of public testing options, and primarily were basing it on their own internal testing which was far higher skill than the average player because of far more play time.
Not just cuz of more playtime, but also because when you're the one designing the game, you know the inner workings.
I'm not some game developer by any means, but even spending some time making a bunch of Super Mario Maker levels really taught me how incredibly easy it is to lose sight of how a normal player might fare with or deal with the challenges you're designing for them. And that's even with trying to keep it in mind. Fact is, you can never go back to 'not knowing' about your game/level, so it becomes basically impossible to try and 'imagine' how an outside person will see and deal with it. This is why external playtesting is just so critical. That's not without its own pitfalls, but if you're trying to do everything internally, you're going to get lost in your own world. Fine for making music, or even movies, TV, etc with very prescribed experiences, less so for interactive video games where you rely so much on the end user having to navigate through the experience you designed for them manually.