Doesn't quite work that way.
First of all, in order to have a proper deployment of, say, 1000 crew, accounting for recruiting/training/manning shore establishments of all sorts (including the fleet maintenance groups, dockyard, bases and naval HQ's) you need almost 1.8 persons ashore for each sea position. Anything lower and you start having to send crew to sea over and over again, depriving them of their proper ratio of time ashore.
Second, we currently do not have the crewing you are representing. The HAL's and MCDV are not fully manned and even then they are not all crewed. The submarines can only put one real operational crew together right now, if pushed came to shove, they might bundle up a second one. Since the objective is to man the fleet as you mention above in the end state of the CSC's entry into service, then it is more than 1000 extra crew that you have to qualify, plus the then multiplication I mention above to maintain proper sea/shore ratio.
Finally, even if what you indicate was the case, it is not the way to look at it. All crewing issues come down to a breakdown of various trades and their criticality. If everyone was up to scratch in levels but the MarEng Techs were at 50 %, you still couldn't operate all the ships even if you wanted to. So each trade as to be looked at in isolation, and right now, the technical trades are definitely the ones hurting the most.