But Improvement! So? You think it can't be capped or slowed down?
First, why so snippy? You asked for advice and input, but then get aggressive at anyone who says anything that disagrees with your original premise.
Second, of course you can cap and slow things down. Where did I say you could not? I was offering general design advice to fit the genre because you’ve presented no specific mechanics to discuss one way or the other.
That said, you’ve said you intend to base your system off OSR rules, so some flavor of TSR D&D is the presumed starting point or its not “OSR-based.”
And the reason I find that a bad fit is that level-based advancement tends to drop a bunch of stuff all at once when you level vs. the granularity of improving one skill by one rank every session or so.
When you slow down level-based progression it means longer stretches where your character is static. In skill-based progression you can still have a feeling of progress be because going from rolling 5d6 to 5d6+1 for one skill (of dozens) is still an improvement, even if it’s tiny relative to the PC as a whole.
Similarly, if levels are capped, once you reach that cap you’re basically done in terms of improvement. With skills, once you cap your primary ones you can always move on towards picking up new skills and getting those to the cap.
Honestly, I think you’re doing yourself a bit of a disservice in terms of game design in not wanting to even look at systems outside of the OSR; particularly when there are already systems that model the genre you intend to write a game for. Seeing how other people have solved for a particular problem can better inform your decisions within your own system, particularly if you want to avoid repeating the mistakes made by previous attempts.
Limiting the scope of your options to the OSR is roughly akin to believing Palladium’s Robotech game is the pinnacle of mecha combat rpgs while never even looking at Mekton or Jovian Chronicles/Heavy Gear, Battletech/Mechwarrior or the rules for mecha in d20 Future (or even mechanics from the Mechwarrior Clix for that matter).
But if you’ve already made up your mind, why ask in the first place? Just get to writing and/or share with us your progress and/or concepts.