From watching Teeth play a couple times I'm sure he uses inverted because it makes stabbing with long polearms easier to abuse, since you aim up release then drag down, without colliding on terrain or anything.
Chambering is tough with inverted, and connecting too early in a swing and glancing happened to me a lot too. I prob never really adjusted my footwork for proper inverse hilt slash abuse though, since I used normal for years and inverse for several months, but eventually went back to normal.
I feel like normal gives you more sense of control on your offense, and easier to target switch to your sides. Inverse definitely makes attacking people in front of you easier though, good for OP noob support polearms (Teeth) or facehug hilt slashing/wild spam.
Also 1hand + shield isn't underpowered as a playstyle, just really shitty players tend to play it and cry about 2hand and polearms being OP, as always.
edit: HEY CMP is it possible to have control options of inversing stabs and overheads, but keeping sideswings the same? THANKS