I would always want the option of removing or adjusting tips for poor service. Forty plus cruises and one time removed tips from waitstaff.
DW has unusual food allergies and we go over them very carefully with waitstaff and she carefully orders dinner for the next night each day.
This waitstaff made error after error. One of her triggers is green vegetables. She order chicken and carefully reminds them no spinach. The next night her entre comes to the table with the chicken covered in spinach, We point this out to the headwaiter and all he does is shrug his shoulders as not my fault even though he was the one who put it in front of her. That was inexcusable/
We called over MD who profusely apologized and he could not do enough for us. We had dinner the next night on lido and they sent us a rather special dinner and sent a bottle of wine and cheese plate to our cabin.
This was the only time we removed waitstaff tips. Normally hand out cash last night as deserved. Also mentioned the waiter very prominently in our comment survey.