The actual amount of the suggested tips is comparatively small compared to staying in a land-based resort in the U.S. It's only being surprised that is unpleasant. On your next cruise you will know what to expect.
You should absolutely feel free to tip less or not at all if you were unhappy with the service. On one cruise I received minimal service from the cabin steward and did not tip him. Usually the waiters are so good I give extra.
Also, I always order expensive bottles of wine and reduce the tip on those through the purser before disembarking. I think $5/bottle is plenty to tip on wine.