Ok the idea i had is basically that for each tier of difficulty, you get a certain amount of points for each difficulty, once you have enough points you unlock the final difficulty in that tier, upon beating it you advance to the next teir.
so lets say you the amount was 45 points to unlock difficulty 10
you beat difficulty 1, you get 1/45 points and the ability to access difficulty 2
you beat difficulty 2, you get 2 points, added to the 1 you already have, 3/45 to access difficulty 10
you beat difficulty 3, you get 3 points, and are now at 6/45
so now, you are looking for a level 4 game, but none are happening, you see a difficulty 3 game, you join and win
you get 3 more points and are at 9/45, 1 more point to unlock difficulty 5, and 36 more for 10.
now of course with this system one could beat level 1, 45 times to access level 10, but to be honest if you beat level 1 45 times, you are probably ready for level 10.
now the system resets for the next tier,
you need 45 tier two points to access level 20 11 gives you 1 point, etc.
so would there be some seperation, yeah, but not as much it would basically be hard seperated by 1-10 11-20 21-30 etc, with a soft seperation in between, notice as well 45 points is 1+2+3+4+5+6+7+8+9, which means you would never have to repeat a difficulty to progress if you didnt want to.
side note, i think that each tier difficulty should be unlocked at the proper number if you had got up there normally, like
tier 4 would unlock at 10/45 (1+2+3+4)
tier 7 would unlock at 28/45 (1,2,3,4,5,6,7 sum)