Being a part of military actually should be seen as a limitation rather than William going his own way. Since the soldiers pledge their loyalty to the crown it is deemed appropriate that a potential future monarch should serve in the military. They get to choose which bit, and perhaps when, but they probably never had a choice about joining up. Then the Royals only tend to spend a couple of years. Harry is the keenest as he joined infantry. But his fame brought him back from action early because he was a prized target.
Also Wikipedia now says Harry's now in project management: "On 17 January 2014, the Ministry of Defence announced that Harry had completed his attachment to 3 Regiment Army Air Corps and will take up a staff officer role at the position of SO3 (Defence Engagement) in HQ London District. His responsibilities will include helping to co-ordinate significant projects and commemorative events involving the Army in London."
I would expect this is not what he would have chosen had he been born Harry Smith.