I've wondered for some time now if Wormwood was inspired by pikmin. The greater vegetative mass increase normally doesn't make sense, but is of vital importance in the pikmin series. There blooming not only increases the speed of running but also the damage dealt.
Wormwood is covered from head to toe by his blooming which we can assume is making him "lighter". If his arms where to follow the same empowerment as his legs then it stand to reason that he should attack faster.
Balance:
Now that wormwoods hunger drain has been greatly decreased, this downside can be re-instated in a different way. When Wormwood attacks in bloom he will drain hunger in a similar fashion as Winnona's crafting (but hopefully weaker). This would pair wonderfully with his other perks. Attack speed is a lesser combat oriented perk in comparison to a raw damage increase. The faster you attack the faster you consume the durability of your weapon; it has a self-inflicted balance (hambat is the exception). Allowing him just one extra hit, while essentially a 30% damage increase in some scenerios, would not be out of place with combat perks other characters have obtained in their reworks.