User blog comment:Commander Marko/Do Ranked KDA stats mean that much?/@comment-9937664-20140616144422/@comment-25055281-20140616224706

Two scenarios:

1_Player A with kda 4.0 in silver and player B with kda 4.0 in platinum. B is probably better as he has that kda vs more skilled competition.

2_Players A and B both on the same tier and division, A kda 4.0, B kda 2.0, A win% 50, B win% 60...if the number of games is not too small, B is probably a better player and will climb the ladder faster.

Of course the data available from Riot are limited (althought they announced a new "History") but you could aproximate win% from number of games won or LP in some circumstances.