It will affect EVERY SINGLE PERSON who plays it for PC and uses inverted Y-axis controls for flying/character control
That is correct. I'm used to a non-inverted camera, and switching it in the Xbox version of DKS made flight very hard to control. While I started getting used to it a bit, I doubt I would be very effective during combat.
- which is most people.
This I have to disagree with. Nobody in the forum reported a problem in the PC version of DKS, and only a few since D2:DC was released.
Considering the fact that this is an incredibly simple problem, I see no reason Larian can't release a small patch to address it.
The patch process is fairly involved, including QA across all the different language versions (and you're right that QA for DKS or D2:DC should have caught this), and then updates for everywhere it was released, etc. I suggested a hotfix for those effected rather than an official patch, but quick fixes are not necessarily quick, and that would cause extra complexity for any future patches.
Also, the inverter program you mentioned (Polynomial's) doesn't work for this problem.
Sorry about that.
