Let's assess the worth of the chainsaw and katana in the various situations a berserker finds himself in:
Settings: 6p suicidal
Assumptions: Chainsaw primary head shots are useless as they allow the specimen to survive (while decapitated). Katana grants increased swing speed compared to chainsaw secondary, and grants a big movement speed bonus.
1. Holding a position
1a. With no room to back up
- Katana - Can bodyshot-kill clots and crawlers. Bodyshots stun gorefasts. Headshots kill gorefasts, sirens, and husks. No weaknesses.
- Chainsaw - Bodyshots kill everything below husks. Swings speed results in a few specimen piling up and hitting you before you can kill them. Theoretically possible to kill crawlers before they hit you, but unreliable.
Winner: Katana
1b. With room to back up
Winner: Katana
2. On The Run
Winner: Katana
3. Against the Big Guys
3a. Scrakes
You can kill them with both
Tie
3b. Fleshpounds
- Katana - When a FP is low on health and rushing you, high swing speed and headshot damage, coupled with possibility to back up quickly while attacking, makes this a reliable, though sometimes costly, way to deal with FP.
- Chainsaw - Slow swing speed, low HS damage, slow movement.
Winner: Katana
Katana wins 5-1 against chainsaw.
They both suck at holding your ground with no room to back up, but katana sucks slightly less. If chainsaw had the capacity to kill gorefasts and clots on decapitation, I could see it far out perform katana in a small area. You could kill everything rushing with primary, and take the medium sizes out with secondary.
Since we currently have to dedicate a secondary chainsaw shot to kill the small stuff, the slow swing speed of the chainsaw results in berserkers taking unnecessary damage. In a group of 3 gorefasts rushing the chainsaw berserker, the first dies immediately, the second dies right before his swing lands, and the third gets a full hit in. Throw in anything else, such as crawlers or clots, and more damage is taken.