But it doesn't average out. The 5ms player is continuosly 4ms behind the other player. As above poster explained - the times add up. So you have 200ms + one to five ms. If server tick is as little as 5ms the problem is even worse as in that case player A will with exact same reactions get a faster tick in 4 out of 5 times. I don't know how often it matters, but I'd expect top player to have pretty similar reaction times. So let's say 2 opponents are both between 200 and 220 ms reaction time - then constantly having 4ms more for one player definitely sounds like it will have an effect.

edit: Or in other words - it depends on how often the reaction of the opponents is with the 4ms difference. That certainly depends on the game and the players.