In this reproduction attempt we see:
dplyrtime being around 0.05 seconds. This is about 5 times slower than claimed.
sum()/n()time is about 0.2 seconds, about 5 times faster than claimed.
data.tabletime being around 0.004 seconds. This is about three times as fast as the
dplyrclaims, and over ten times as fast as the actual observed
Read the whole thing. If you want to replicate it yourself, check out the RMarkdown file.