I recently tried leveling a guts/knife build. The whole idea was that the regen skill and healing items would heal me just above mid-health as I took damage enough to fall just below. While I would take dramatically less damage due to the large def and atk boost, this strategy consumed an awful lot of healing items. I found that when I went full dagger and increased the number of SP restore items a bit I cleared faster using less items. Daggers charged attack simply costs so little SP and deals such brutal damage that guts will help, but I wouldn't level the skill past 1 point before daggers would be nearly maxed.

A part of the appeal of guts was that I assumed I could put fewer points into health, but ended up needing more in total to be able to trigger guts consistently and safely in useful situations. I do imagine the brawler can beat the ninja in a speedrun purely on the grounds of damage. My guts brawler was lvl 37 I believe when it started advanced mode and most of the game was very easy, just a bit consumable item dependent.

If you are including advanced mode guts will quickly becomes nearly useless compared to other skills as your gear is not good enough to mitigate enough damage. The amount of stats you need to invest into health to play safely would be better spent on strength so that everything dies from a charge-up.

Sorry for the long rant. TL;DR, you can get brawlers to easily kill things in a single charged attack if you keep investing in STR and daggers. Guts will as such decrease your speed and increase your item dependency. Guts will sometimes give you absurd numbers while playing, like a regular stab dealing 500+ damage from guts triggering multiple times, but with a regular knife focus you would just spin once to kill anyway.