An argument could be made that both then and now too much stuff scales with level, some of which probably shouldn't...or not for all classes.
I'd only entertain that kind of argument if hps scaling with level were on the table. You think the fighter & cleric shouldn't get stealthier with level or have a better chance of solving a puzzle or having picked up a bit of lore? Fine, the magic-user and thief can make do with 1 HD their whole career.
Ridiculous? Nope, skill-based systems went there. RuneQuest, for instance, you advanced in each skill individually, based on how much you used it, and advancement got harder the better you got - a suggestion, at least, of a 'realistic' learning curve. Hit points? Not s'much.
Perhaps...but where it can make any sense, let it do so.
It makes sense that an experienced adventurer gets better at adventuring, so if a check comes up during an adventure, his chance to make it should scale with level. If a check comes up when he's managing his household between adventures, by all means, screw with him.
Not the best example, as again this is something that has its own roll - in this case against the Thief's move silently (and-or hide in shadows, as appropriate) skill.
Actually, that's why it's an excellent example...
And again, the roll-under could easily be modified by the DM. I can't count the number of times my DM has said something like "That's hard to do. Roll under half your {stat}."
It'd be pretty hard to sneak past that sentry, he's fairly alert. Roll under half your DEX.
DEX 12 whatever (magic-user, hobo, you name it) needs a 6, 30% chance of success.
DEX 18 1st level thief needs to roll his move silently and hide in shodows separately and mak both of them. I'm not going to dig up my PH, but I'm guessing something around 9-20% chance of success, in aggregate. Or, the DM could take pitty and and let him roll under half DEX, like everyone else, a 45% chance.
(And, it's a fool's errand, anyway, since someone in the party is going to fail that roll and blow the whole thing.)
I don't mind different systems for different things provided there's some rationale for it and provided the system in use does the job.
Any d20 check boils down to a flat % chance of success, just one divisible by 5. d%, likewise, just you can roll a 23% instead of choosing between 20 or 25. (yippee)
Roll-under can be rationalized as making stats relevant (and yes, reducing the relevance of level sometimes) no matter what they are.
By doubling their impact relative to d20 bonuses, and making them all-important in the 1e version.
The d20 standardization model suffers from the designers coming up with what is a good idea for some situations and then trying to shoehorn far too many other things into it, things that would be better served having or retaining their own unique resolution system.
Any resolution system that gives a random result with a linear distribution can probably be done fine with the d20 core mechanic. That includes roll-under and roll-high-without-going-over and d% resolutions.
It does not include bell-curve distributions, like 3d6, let alone more sophisticated mechanics like dice pools, traits, complications, etc, etc...
For another example of this, see advantage-disadvantage in 5e. A third example is trying to use the hit point mechanic to cover everything that can ever happen to a character where some effects should bypass hit points entirely.
Those are all examples of better game design than we had back in the day, yes. ;P
Back to roll-under for a minute: one place we've found it works really well is consciousness checks. If you're at or below 0 h.p. (in our game death is at -10) you need to roll your Constitution score, modified by your current h.p. total, or less on a d20 in order to remain conscious. So, if you're Con 12 and you've been clobbered to -5 you need to roll (12 - 5 = ) 7 or less in order to stay conscious. 20 always fails.
How 'bout death at negative CON, roll over your current negative hps without rolling over your CON to stay conscious?
