Cruised for over 40 years and for most of that time paid the gratuities recommended or withheld as the whole process evolved into what its become today. Then when the increases started to be frequent and not just the $0.25 change but several dollars (i.e. NCL jump to $20) it reached a boiling point. One day room service, reduction in food quality and choice, etc.etc. etc. we said no more.
We don't buy into tipping behind the scenes workers and people we wouldn't tip on a land vacation so we now remove the prepaid and tip the waiters, bus boys, cabin stewards and bar tenders directly and never received negative service.
The other thing that irks me is the blanketed amounts that every cabin pays either $18 for balconies and below and $20.50 for suites and above as if its logical amounts. Seems to me the gratuity should be based on what you are getting such as better food (coastal kitchen) and larger staterooms and should be based on your cruise price. I just looked up a random 7 day cruise out of NJ and the cost of the cheapest room is just under $1,700 (for two) compared to a suite at over $4,000 for a couple.
If I went into any restaurant and ordered hamburgers that cost $25 and the table next to me ordered steak at $100 our tips would be very different, why are the cruise lines different? Well, because they made it up and and play on our emotions.
There's no right or wrong answer here, do what you feel is best and it will be fine.