Skill points don't have diminished returns. People are confusing that expertise spent on skills has diminishing returns- ie: the green yellow red bar where spending expertise beyond your first three ranks nets you less skills per *rank* than the first three.


Your first three ranks in a skill grant you +18 skill points per rank. Your next three beyond that grants you +10 skill points per rank. Your final three, up to a total of nine ranks, each grant you +5 skill points per rank.


Thus it can be said that skills have diminishing returns, but only when you buy them with your skill ranks. The actual skill points themselves do not have an innate diminishing return.