OH25shooter, I did read your post, you made a flat statement "Any degree of cant is illegal." with no mention of where you got that nonsense. I am not going to Ohio to read the rules to the "instructors" wrong though they are, but I will quote some of the actual IDPA holster rules for your and Glocknation's convenience and clarification:
http://www.idpa.com/Documents/IDPARuleBook2005.pdf
page 33-34
Holsters:
D. Must carry the firearm in a neutral (vertical) or muzzle rear
cant, but have no adjustable cant backpieces. Holster cant that
is adjustable by removing bolts and repositioning the backpiece
is allowed.
NOT Permitted:
E. Muzzle forward or ‘on the belt’ adjustable cant holsters.
Those that allow the cant to be adjusted by the shooter while
the holster is on the belt are not allowed.
NOTE: Holsters with an adjustable cant via removal of bolts
and repositioning of the backpiece are approved if set for
neutral or muzzle rear cant.
I think you will conclude that anything you heard to the effect that "Any degree of cant is illegal." is just flat wrong according to the published rules. True, a muzzle forward fastdraw cant is not allowed, but the usual carry rig "FBI" cant is allowed and is popular.
Unfortunately, such stuff is all too common in IDPA matches, or those being called "IDPA style". The operators don't know the rules or don't like them so they make up their own.
You gained another false impression: "Talking to the competitors it seems anything is legal, because you are placed in classes according to the firearm you use." is not correct. There are five firearms Divisions and each is rather closely defined. A lot of us got rather bent out of shape when they reduced the maximum revolver barrel length from 5 inches - the most common on S&W 625s at the time of IDPA's founding - to four. Weight limits have been tightened up, too. I had to take the steel-backed neoprene Pachmayr grip off my CDP .45 to qualify.