i ask the same question with a zone team i coach with a guy in d1. zone is the only off or def i haven't won with, so im not the best source, but it seems pretty decent to me when the talent disparity between your players is large. i think its disadvantaged in championship play across the board, especially in d1, because the depth of talent on top teams tends to be very substantial, where getting more minutes to a starter over the backup just isn't that useful. zone isn't as common as other sets, and i think it is a good set, very possibly the best set, for a number of rebuilding situations - but you still hardly ever see zone teams win titles it seems.
anyway looking at your team, you have some good players but zone definitely suggests, to me, teams should be doing everything in their power to get super stars. studs go further on zone teams than in other defenses, taking walkons as necessary to accomplish this is worthwhile. i think you could do a bit more on that front. overall the talent gap wasn't as big as the seeding suggests, which happens all the time, so thats probably part of it, too (that and a little bad luck). that said, the one thing that really sticks out is rebounding. your rebounding is really bad for a d2 team, it seems to me, and you are getting killed on the boards over it (if you look at your team overall, and are seeing that +1 reb in your favor on team stats with that #2 sos, and not understanding why i still say you are getting killed on the board, let me know, and ill elaborate). zone is weaker than man on the boards in the first place, with those rebounding rating, its trouble. losing to a press team who has huge advantages over you in TOs and rebounds is going to be VERY easy. your offense/defense quality just in terms of shooting on both sides can overcome some of that stuff but its so easy to not have a great off/def night, and lose games, when you have to substantially beat the other team on raw off shooting/opponent shooting def just to break even.