I'd say your conclusions about "IDPA cover" are informed by your one match experience.
The new IDPA cover rules have generally resulted in much more generous exposure of the shooter to the target than was the case pre-2017.
Because you used to have to adjust cover for each target, while today you have a single cover line for every target in a given array, there will usually be only one target with cover that is tight, and you then find that you can assume a position that leaves you completely exposed to a target or targets at the opposite end.
If you shoot the new IDPA classifier, you'll see that when you are shooting from the cover of the barricade or the barrel, you can see all three targets simultaneously, and Tactical Priority is merely engaging left-to-right or right-to-left, rather than being a matter of engaging the only target that you can see, as was often the case in the past.
Each stage's procedure will dictate whether you must wear the vest or not; why would you think it was the shooter's option? Or, why would you be surprised when you discovered there was a rule that didn't allow the shooter to decide?
IDPA, in the last four or five years, has changed dramatically. It's a very different sport than it used to be. Easier to shoot, easier to officiate, fewer rules, but it's missing a lot of what made it a unique sport, and it's less distinct alternative to other shooting competition/entertainment.