I agree with some of your sentiment, but I think you don't have accurate information on all of the military. The big deal with the reserves/NG (in the Army, at least) is that there is a huge difference among units; the majority of army PSYOPs capability is actually in the reserve component, and is as good as anything in active duty; there are both active duty and reserve units in other specialties which are pretty widely regarded as incapable/ineffective. It kind of becomes an evaporative cooling thing -- good people who end up in bad units find ways to leave, and are attracted to great units. Basically the same as companies in the civilian world.
In some cases, the services (and government as a whole, and big companies) don't take advantage of pre-existing skills or aptitudes. In other cases, they do -- there are incentive/recruiting/fast-track systems for certain types of professionals. They've gotten better about this since becoming an all-volunteer force vs. draft. The big problem is that there is a "military way" to do a lot of things, largely focused on big-vendor enterprise in the IT space, and you have to work within that. Getting affiliated with a lab, DARPA, etc. is probably the way to use more interesting tech.
One problem I have personally is that they're very credential-focused; as a high school and college dropout, I'd be kind of screwed. Otherwise I'd be really interested in reserve/NG in certain specialties (psyops, civil affairs, infrastructure parts of embedded advisor teams, rotary/uav aviation, sigint, SAR, medical, diving). It would also be really difficult for a startup founder vs. an employee at a larger tech company.
For the donation/volunteer argument, rather than just donating money, my plan is to do NGO work on the side, and hopefully eventually be able to set up a specialty communications-in-conflict/disaster zones infrastructure NGO. A lot of charities ARE saddled by large numbers of unskilled volunteers (or at least without specific relevant skills), and structure their operations to be labor vs. skill intensive.