The reason that there is “hundreds of Gt being calved” is because there is a huge excess of snow and ice in the interior, which is being pushed to the sea by its own weight. We have watched more than a metre accumulate at the Greenland Country Club over the last year, forcing them to relocate the club house.
If the amount of ice accumulating in the interior decreased, then the amount of ice flowing to the sea would also diminish. If surface melt exactly equaled accumulation, then eventually calving would slow down to zero and the amount of ice would remain constant.
This is a typical mistake made by alarmists. Combine mutually exclusive worst case possibilities into an impossible disaster scenario.