I disagree with your logic.
Firstly: that D&D is or should be historic. D&D is mythic. In myths, there are many warriors (read: fighters) who overcome the magical enemies. I will grant that some of them have little to no skills or abilities beyond fighting though. Being that the only example I can think of to fit that exception is Beowulf though, I think he may just be the exception to the rule.
Actually, realistic or mythic, warriors of the various eras are quite skilled in various domains.
Prior to standing armies, they were hunters, raiders and leaders. Fundamental skills of awareness, tracking, animal lore and environment lore were vital to survival, and the ability to manage followers, issue orders and quell dissent are things they sorta just picked up as they went.
Legendary heroes of this era were usually possessed of some additional skill, whether smithing or some other finer pursuits. Its what distinguishes them from the run of the mill tough.
Later on, with professional armies and nobility, theres a bit of a split between commanders and foot soldiers. Foot would be familiar with wilderness lore, field tactics and, first aid, along with the basics of ground level command, while losing a bit on awareness, making it up with quantity. Officers(and thus, nobles) were leaders first and warriors second, so arguably no longer necessarily Fighters. Theres also a lot more specialization. Modern armies still operate along these lines for the most part, just consider the kind of skills a professional modern soldier is expected to have some mastery of.
The 3.5 Fighter as we see it though, is the province of the conscript. The peasant, who for the lack of being more valuable in another trade, and not powerful/rich enough to have a command, is given basic weapons and gear, and trained as part of a formation more than as an individual. This is funny because we do have such a class, the NPC Warrior class is supposed to be for conscripts and militia I think?
I'm thinking for out of combat competencies, you'd need to split into areas of competence, as well as progressions to measure by:
-Extended combat competencies. Combat-related abilities that are significant out of combat. These include perception (heroic, and notable famous warriors are generally quite keen of senses), endurance, and feats of athletics. Stuff any serious fighter could be expected to be good at because they are closely related to actually fighting.
-Survival competencies. Any army dependent on forage, or which even operates outside a parade ground at all has these. They're the ability to obtain basic food, shelter and water out of the environment, the ability to navigate an unfamiliar area, and the ability to pass without notice. First aid also goes here, whether treating yourself or an ally, war is a trade where people get injured regularly, and medic or not, first aid, caring for injuries, and dealing with stuff like common poisons or wound infections are standard skills by necessity.
-Maintenance competencies. Basic to advanced smithing/fletching abilities, the ability to make sure your gear keeps working. An oddball thing, in that some degree of personal gear upkeep is expected, but barring the odd legend, few actually become legendary craftsmen.
-Tactical competencies. Simply put, squad or individual level tactics. Outside of combat, it again involves a grasp of terrain, how to use or modify it, as well as more general planning and problem solving abilities. Predicting short term enemy movements also fall inside this somewhat, as does preparing a rest area or campsite or sensing a ruse/ambush/trap. Level dependent, experienced fighters are expected to be able to do this, but lower level ones might not know much.
-Strategic competencies. Large scale planning, an understanding of logistics and general ability to organize or anticipate the organization of things beyond the scale of a single party. The ability to identify the plans and motives of others. Lots of overlaps with tactics and also level dependent.
-Leadership competencies. Command, intimidation, how to project yourself so you seem threatening or imposing. Sort of a given with most types of fighters, its mostly just how you motivate and order people around.
-Command competencies. The strategy to leadership's tactics. Politics, diplomacy and the various associated knowledge needed to govern men and nations properly.
Note that no one fighter is necessarily good at all of these, or even great at the ones they can do, but any fighter should have a big chunk of them at varying levels of competence. And these are mainly niche, backup or required skills, not ace skills (that is, character defining abilities). They are improved by everyone in the team having some of them, rather than made redundant.