I suppose people may differ as to whether arrogance that corresponds to actual excellence is more or less irritating than arrogance that corresponds to no actual excellence, but surely we've all seen it many times in cases where the arrogant person wasn't actually superior--or not superior enough to warrant their confidence.
I've come across both and only the first type is annoying. The second can first be mistaken as the first but then get to know them as being very enthusiastic and inexperienced (not knowing what they don't know).
Also confidence IMHO is a totally different thing and doesn't manifest itself the same way arrogance does.
For example saying: "My team is really good" displays confidence in your team, saying "We can beat the crap out of every other team easily" is arrogant, even if it's true.