go and read the items stats in the game data the attack that the sickle uses adds def into the comparison sicklenormal adds +2 atk and +2 def to the comparison while shortsword adds +5 atk and +2 def to the comparison which could be more easily be expressed as
Sickle = atk+0 and shortsword = atk+3
the files are sicklenormal and shortswordnormal
which is to say the sickle does less damage just in general but its only like 2 atk worth of damage