Sorry to hear about your cruise. Just so everyone knows, the booking of large groups is not limited to just one cruise line. There was a group on our last cruise (a different cruise line), although they were not as visible as the group you describe.
Sometimes, a cruise line might charter a ship for the entire group. This happened to us last year -- we were given a small credit to rebook for another date. Yet, there are other times that the group isn't large enough for a full-ship charter.
One tip someone once gave me was, when booking a cruise, to do an Internet search of the cruise date to see what comes up. Of course, this won't help you now, but may be useful in the future.
Another tip is to take care of any issues while onboard -- bring them to the attention of someone who can do something about it. We've had to do that and it was almost always dealt with promptly.
As to what to do now -- I'm not sure we can offer any advice other than what you've already done. Don't write off Royal Caribbean -- your next cruise with them may be a return of what you'd grown accustomed to.
I do encourage you to stick around our forum. But, even if you don't return, I hope the tips I noted above are useful to anyone reading this.