When Dark Sun came out, it did something radical for the time. It started every chaacter at level 3 because characters of lower levels just weren;t togh enough to survive in the mystical post-apocalyptic desert of the setting.
I thought it was cool that everyone was tougher, but didn't think much more of it at the time.
In retrospect, it didn;t really matter that the character's were tougher and more proficient, because everyone was tougher and more proficient. Unless you were doing some kind of Spelljammer or Planescape campaign where characters would interact with "weaker" characters from other settings then everyone just scaled up accordingly and the enemies you faced were still rougly pound-for-pound just as difficult as enemies you'd face elsewhere.
But third level also meant that the numbers averaged out a bit. Instead of a wild mix of hit point possibilities induced by a flat die roll at level 1 (I don't know of anyone playing with the "Level 1 = max hit points" option), you'd get a bell curve from the rolling of 3 dice and adding the results.
It also basically meant that the power difference when you gained a level wasn't as dramatic. From level 1 to level 2 can be a massive jump in power (doubling hit points, more powerful and more frequent spells, increased potential to hit someone), but the jump from level 3 to level 4 is more gradual. Arguably, levels 5-10 were the sweet spot for D&D anyway, so this helped to alleviate the boring bits needed to get to the "action".
But for the purposes of "Other Strangness" which is a step away from all of that I'm considering the idea of starting levels a bit differently.
If I'm working off the system that characters get to roll a number of dice every turn equal to their current stance. Then we could give everyone a single stance point at the start of the campaign, a character with a bonus in an attribute would have two points, maybe even three. That first bonus basically doubles the amount of actions you can take (or doubles your chance of success if you roll those dice together), a second bonus gives you triple the base number of actions. For heroic heroes against regular mortals this might be great, but I'm not sure that's the way I want to go.
If I started everyone at "level 3", with 3 points in every stance, then that first bonus would give a character actions matching their regular opponent but after every third action of their opponent the hero would get two consecutive strikes...or they could match their opponent action for action and once ever three actions they could roll two dice together for a more powerful result. The first degree of benefit isn't as powerful, but still has potential to be a game changer if worked right.
I could push it even further, giving everyone 5 or even 10 levels in their stances, but this would really reduce the mpact of any benefits. For something dark and gritty, that might be the way to go, but for something a bit more heroic, I'm thinking that the "3 levels" option fits my current thoughts.
Regular folk on the street might only have 2 levels, just to confirm that these are mutant beings more powerful and dangerous than the average citizen.