You have had 3 separate reports of Exchange being borked in the same way, and in at least 2 cases knowledge that it was being escalated as far as the company knew how. (In at least one case, Microsoft tried to figure it out and failed.) But you're saying that what is described can't be happening because it didn't happen to you when you did things properly.
What this means to me is that there is some bug in Exchange that under some circumstances causes double-booking to become a real issue. You didn't encounter that. Fine. I believe you. All that that means is that you didn't encounter that. You have no idea what triggers the misbehaviour, or whether you could solve it if it happened to you. You have no idea whether your avoiding it was due to some step you did right that they did wrong, or due to blind luck that your setup didn't trigger the bug. You know none of this because you've not seen the problem.
So you proceed to compliment yourself and blame the victims, with zero evidence.
But, for at least 3 people here, the fact is that Exchange does not book rooms properly. It double-books. It therefore is not going to be perceived as reliable.
If that experience is widespread, then Exchange could be very vulnerable to an alternative (any alternative) that solves the same problem and doesn't give bad results for as many people.