The manpower issue is I suspect, less to do with Treasury investment and more to do with political and institutional reluctance to make certain decisions. The manpower crisis is two-fold - insufficient overall headcount allowance, combined with specific pinch-point / experiential retention issues, which combined have a multiplier effect. The first is absolutely down to reluctance to increase overall AF headcount following the 2010SDSR and a similar reluctance to grasp the "what sort of army do we need?" nettle. The second is possibly an indirect result of the first, with endless back to back deployments etc, which hits in the hardest to replace part of the manning plot.
The Navy are at least trying to make the best of its headcount allowance - although the proof will be in the pudding, given the methods being used. I'm sure RAF are doing the same.
I'm not sure certain constituencies have yet agreed that we should be delivering air and naval power in line with our geographic position, which brings us back to the first issue.......