The odd 6-10 hour long intercept is relatively insignificant in the lifespan of a fighter. I don’t know how the USAF tracks fatigue, but intercepts are along the lines of transit flights when it comes to airframe stresses, unless there are other “tactical” manoeuvres required to get behind a bear.
We tend to focus on the equipment but, more often than not, it's the command relationships and doctrine that make for a credible 'tactical air force':
Tactical Air Power Controversies in Normandy: A Question of Doctrine
A Compromise: "Joint Command"
Notwithstanding the progress being made at the operational and tactical levels, fierce Army/RAF disputes over command and control of air forces continued. The Army was keen to have air forces for ground support organic to their own service, or at least unde r Army command.
This the RAF stoutly resisted, and even while the new tactical air force idea was coming together in North Africa the bureaucratic turf war over command and control escalated all the way up to Churchill himself. He produced a compromise slightly favourable to the RAF. Contrary to the Air Staffs original wishes, a considerable portion of the RAF's resources would be devoted specifically to army support in the tactical air forces. But against the Army's demand, these air forces earmarked for army support would remain a part of the RAF, under sole RAF command . The Army and RAF remained separate services, and they operated under separate commanders, even in the furtherance of one combined plan .
As contemporary doctrine put it: The Army Commander tells the Air Force Commander what he wants to achieve, and the Air Staff, having examined the problem, make Air plans with the Army's aim constantly in view. Under this system, headquarters were paired at each level of command . For Operation Overlord, 2nd Tactical Air Force (TAF) itself was in support of Montgomery's 21st Army Group, and both of these formations had a headquarters which were deemed to be co-equal.
At the next level down, 83 Group and 84 Group were to be in support of Second British and First Canadian Armies respectively. This arrangement is important, because the principle of joint command meant that contrary to the Army's wishes, at no level could Army commanders order air support. Air forces were never under the command of Army commanders; both services remained under their own, completely separate, chains of command. In fact, the lowest level at which the two chains of command met was in the person of the Supreme Commander himself, General Dwight Eisenhower. As Brigadier Mann's accusations make clear, this was a contentious issue.