I have read several times that surviving arming swords/knightly swords often exhibit more profile taper than they had when they were forged because of continued sharpening throughout their period of use. To my knowledge these swords were sidearms so although they were carried all the time they wouldn't see a lot of use in actual combat. If use in combat was not the primary cause of the blade to require sharpening than why were they sharpened often enough to effect the silhouette of the blade?

A lot of people will say something like "swords were never primary weapons" but that's really an over-simplification, probably in large part driven by a desire to feel like one is "in the know" by finding fault with some particular concept or another. It reminds me of how 15 years ago everything was automatically attributed to "fashion" without many other considerations taken into account. Swords weren't primary weapons in the same way that rifles aren't primary weapons for modern armies, most actual casualties are in inflicted by artillery and that's been the case for a very long time, perhaps even before the gunpowder era. It would be just as absurd now to send infantry soldiers into the field without rifles as it would have been to send Medieval warriors into battle without a sword, mace, axe or similar even if most of the enemy casualties would likely be inflicted by artillery or polearms. Trying to apply concepts like "primary weapon" and "secondary weapon" isn't a good way to look at the situation anyway because it's less like one particular weapon is the clearly favored choice and a lot more like you have to use the correct tool for the job. No matter what ideas might be presented today the fact remains that swords were seen as important individual equipment, they were mass-manufactured century after century and we have ample evidence that they were getting used for their intended purpose.

Perhaps not in every circumstance but any way you cut it the concept doesn't really apply the way it is often presented. Different weapons were used for different phases or aspects of combat. I think part of the reason this is a bit of a peeve for me is that it puts the focus on the weapons rather than the troops where it would make more sense. For instance the primary weapon of a pikeman would in fact be a pike but a pike wouldn't be the primary weapon of an archer so the pike itself is not primary/secondary/tertiary it's just a tool for particular sorts of work that may or may not apply to any given troop.

I'm pretty much agreeing with your main observation though, I think. Somehow or another all that wear and tear was accumulating on these weapons so clearly they were seeing some action and chances are good its because they were being used for exactly what they were made and purchased to do.

I think you also must consider that swords were not only used in battle. A great deal of practice was required to become proficient in the use of arms. Certainly wooden substitutes would be used for some training but there would be a lot of work at a pell, feats of arms displays and tourneys et.c. Swords were expensive and so were not likely to be abused as such but equally most men at arms did not own a huge array of blunts and wasters.

The distinction about swords being secondary weapons or sidearms is misleading, because it can give the impression that swords were not commonly used. In most battles involving cavalry, the knights and mounted warriors would make use of their lance until it snapped, and then would use a second and third lance (if they had them) until these back-up lances broke. Once the various lances snapped, the swords would come out and be used for the remainder of the battle. Given, then, that swords were used after lances inevitably broke in battle, words like "secondary" or "backup" seem inappropriate. Swords are just as much primary weapons as lances; knights used their lances first, but the knight may well have spent more time wielding his sword once his lance(s) broke.