Hello. I was asked to post this here, so here goes:
The melee weapons damage is being displayed incorrectly when you have the Big League perk maxed out (5/5). It reads as if the damage decreases from rank 4 to rank 5. I tested this (a little bit) in game and it seems as if it is just a tooltip error. The next time I play for a little longer I'll take the perk and check if the damage actually decreases or not.
On a side note, this page says it actually decreases the damage: http://fallout.wikia.com/wiki/Big_Leagues