From Matthew Berry

Check out the average fantasy points at different levels for running backs and wide receivers from the past five seasons (2015-19):

RB5 -- 287.5 fantasy points
RB10 -- 230.2 fantasy points (19.9% drop from RB5)
RB15 -- 200.5 fantasy points (12.9% drop from RB10)

WR5 -- 289.1 fantasy points
WR10 -- 251.0 fantasy points (13.2% drop from WR5)
WR15 -- 231.5 fantasy points (7.7% drop from WR10)

That's five years of data showing us that the RB position dries up faster than the WR position. We're just talking about lower-tier RB1s and middle-tier RB2s compared with middle-tier WR1s and WR2s. Meanwhile the drop for wideouts is much less significant. From a general point of view over the past five years, WR15 has produced about the same as RB10.