Isn't a 20% skill difference pretty meaningful in most endeavors? Maybe not the difference between unemployment and rock star but being 20% better at sales for example can be quite lucrative.
The league wide batting average in the MLB was .253 in 2013 (first Google result, I'm assuming it doesn't vary all that much between seasons). While you are correct that hitting 0.6% compared to 0.5% doesn't mean much the numbers I responded to were meaningful in an MLB context (.250 vs. .300) so I think it's justified to use relative differences. In fact I think it's more insightful than using absolute numbers. Speaking of a 5% increase in that context is confusing (at least to me :D) when in reality the skill is roughly 20% above league average.
A programmer who is 20% above average will certainly command a premium as will a salesperson.
As I understand it, a baseball player who performs at the average level is already close to being a superstar; most players are below. This is the reason baseball statistics assess players in terms of "wins above replacement" rather than comparison to the average -- it would be very difficult, if you fired a player, to get an average player to fill your vacancy. (You may wonder how this could be, if baseball ability is normally distributed. Baseball ability is normally distributed in the general population, but not among professional baseball players.)
The comment you responded to was making the point that it's massively unrealistic to expect a team to have a win rate too far from 50% because the absolute difference in skill among all players is small (which means that the skill differences are easily overcome by random variation). Relative differences between players aren't relevant to that argument; you'd need to be talking about the relative difference between the size of the absolute skill gap and the effect of day-to-day variation.
