Handicap used to be the way to determine relative ranks within a local group. If there is no longer a relation between handicap and ranks nowadays, ranks have little meaning IMO and it might be replaced by pure Elo ratings based on even game winning statistics alone.
But I don’t think things are that bad. Checking EGD statistics of handicap games, handicap according to rank difference does seem to work to even out winning probability:
Statistics of Handicap Games - strong side all (wins for weak side)
Gr. H 1 H 2 H 3 H 4 H 5 H 6 H 7 H 8 H 9
Diff Wins Tot % Wins Tot % Wins Tot % Wins Tot % Wins Tot % Wins Tot % Wins Tot % Wins Tot % Wins Tot %
--- ----- ----- --- ----- ----- --- ----- ----- --- ----- ----- --- ----- ----- --- ----- ----- --- ----- ----- --- ----- ----- --- ----- ----- ---
1 2296 5463 42 1 1 100
2 1967 5977 33 1584 4080 39
3 1038 3972 26 1053 3095 34 1091 2829 39
4 351 1434 24 642 2473 26 708 2234 32 910 2352 39
5 80 445 18 213 949 22 484 1798 27 500 1640 30 678 1964 35
6 19 150 13 53 231 23 138 644 21 360 1388 26 380 1202 32 567 1575 36
7 4 51 8 12 83 14 36 203 18 102 495 21 295 1097 27 248 891 28 410 1190 34 1 1 100
8 1 18 6 5 38 13 10 63 16 52 181 29 69 398 17 219 807 27 212 720 29 338 1007 34
9 1 7 14 2 18 11 4 35 11 10 72 14 23 110 21 55 333 17 143 575 25 167 509 33 351 1088 32
10 3 10 30 2 10 20 0 17 0 5 34 15 16 92 17 16 124 13 31 240 13 110 475 23 307 1231 25
11 0 8 0 0 6 0 2 10 20 1 11 9 3 35 9 9 59 15 5 34 15 20 152 13 235 1175 20
12 0 1 0 0 1 0 0 4 0 1 5 20 4 24 17 11 55 20 4 24 17 9 38 24 168 1079 16
13 0 3 0 0 3 0 1 4 25 0 1 0 3 12 25 2 38 5 0 10 0 3 16 19 92 769 12
14 0 2 0 0 2 0 0 3 0 3 7 43 0 13 0 0 15 0 0 7 0 64 617 10
15 1 3 33 0 1 0 0 1 0 0 1 0 2 7 29 0 7 0 0 14 0 0 9 0 32 525 6
16 0 3 0 0 1 0 0 2 0 0 1 0 0 1 0 0 11 0 0 2 0 2 5 40 23 380 6
17 0 1 0 0 3 0 0 2 0 0 3 0 9 317 3
18 0 2 0 0 10 0 0 2 0 5 240 2
19 0 3 0 0 1 0 4 184 2
20 0 1 0 6 147 4
21 0 1 0 1 51 2
22 2 43 5
23 0 1 0 1 13 8
24 0 13 0
25 0 4 0
N.B.: Games with handicap greater than the difference of grade between opponents have been ignored
Legend: Gr diff. : difference of grade between opponents
H <n> : games with <n> handicap stones
Wins : number of wins for the weak side (black)
Tot : number of games
% : percentage of wins
records: 737934
Overall, black wins about 45% of properly handicapped games, which is a bit lower than 50%, but that is expected because traditional handicap falls half a stone short of full compensation.
I think OGS posted similar statistics of their handicap games.
Edit: taking data from a longer time period (from 2006). Now black’s winrate is a bit lower (more like 34-42% winrate instead of 45%), suggesting that the handicap fell a bit short to compensate for the skill difference implied by the rank difference, especially for larger handicaps.