What in the world are you talking about?
Canon freely sells parts to anyone willing to pay for them, including independent and authorized repairers. Heck, you or I can call up their parts department and, so long as we know the part number and have a valid credit card, they'll sell and ship any part we wish to us as well.
It's Nikon who won't sell parts to anyone, forces everyone to use their factory repair facilities (and enjoy long waits, slow service and high repair prices). A memo went out last year, that Nikon was discontinuing parts sales to all independent repairers. I've seen the memo from Nikon, shared by some independent repairer acquaintances who had bought parts direct from Nikon in the past. Word came down later that non-factory, "authorized" shops also wouldn't be able to buy most items. I'm a little unclear if they mean only "authorized dealers" and some "authorized repairers" still have access to parts, or not.
But Canon is fine in this regard. There's no problem getting parts from them, if needed.
Besides, unless a part needs to be replaced due to excessive wear and tear or damage, a lens calibration is only a matter of making some adjustments. A quality independent or authorized repairer should have the proper tools and knowhow to test the lens and make the necessary adjustments.
Based upon cases here on POTN, by far the number one cause of "soft 100-400" complaints is filters. Even good ones. This lens does not like filters. Many people who have mistakenly put "protection filters" on their 100-400 - even the highest quality, multi-coated filters - then been pleasantly surprised how much better the lens is without any filter at all. The lens hood should be used because it might help a bit with focus accuracy and image qualities by reducing any flare, which can effect contrast and color saturation.
Fluourescent lighting is also generally a bad thing. Common household FL bulbs cycle on and off about 60X a second. This often causes metering errors and can mess with focus as well. There are "stabilized" FL bulbs specifically for photography, but they are much more expensive than household bulbs, and nowhere near as widely available.
As others have noted, 1/5 second is an awfully slow a shutter speed for testing. In fact, Canon posted a white paper that the 18MP cameras seem more subject to shake blur. They recommend using slightly higher than usual shutter speeds as much as possible. In addition, 1/5 second is a dangerous speed due to mirror shake. It's right smack in the middle of the range where vibrations caused by mirror slap can have an effect on image sharpness. Roughly from 1/30 or 1/15 to 2 seconds, one should lock up the mirror whenever possible. Live View gives the same effect (so long as you don't use "Quick Focus" in Live View). Shorter shutter speeds avoid the problem. Longer shutter speeds, too, because any vibration from the mirror is only a small portion of the overall exposure and unlikely to have much effect.
And, the 100-400 is one of the lenses that can't self-detect when it's solidly locked down on a tripod, doesn't turn off IS automatically when there is no movement of the lens, so you have to turn off IS manually. If you forget and leave it on, it will induce movement and cause blur. It usually causes a lot more blur effects than what's seen in your images, though.
Another thing that happens is dirty camera sensors. When was your 7D's sensor last cleaned? If one uses larger apertures most of the time, and depending upon what they are shooting and if "dust delete" is enabled, actual specks of dust might not be noticed in images. But an overall softness of images might be due to loss of fine detail, lowered resolution, due to crud on the camera's sensor. Of course, you might expect to see some effect with all your lenses, though it might be more obvious with one than with others.
And, have you Micro Focus Adjusted the lens? It could be that would help a lot, too. Cameras AF systems get out of calibration, too, over time and with use. MFA might correct for that, so long as the camera isn't too far off. If off more than MFA can correct, the camera might need servicing, too.
Testing a lens for sharpness, you want to eliminate as many variables as possible. Hence, good light, a solid tripod, with this particular lens IS turned off, a good target, a reasonable shutter speed, mirror lockup or Live View are all important. Also, if you are not testing focus accuracy, use Live View focusing... it's slow, so may not be as usable in the field. But it is the most accurate form of AF on these cameras. One Shot is pretty good, too. Don't use AI Servo, which is a continuous form of focus for moving subjects, but not as precise. On 7D, you should use Single Point or Spot Focus mode. The center point is best. Or, you can manually focus (though the 7D's viewfinder isn't very manual focus friendly, so you might need an anglefinder or need to use Live View highly magnified). Tests should be done at a variety of apertures, focus distances, and in the case of a zoom, different focal lengths. If you don't tend to use the lens at it's minimum focus distance, why test it there? Test it at more logical distances... the distances you use in real world shooting.
Of course, it can be a fault with the lens. Canon service or any other repairer might not get it right (they are human, after all). Plus with the lens travelling to and fro bouncing around in the back of a UPS or Fedex truck bad things can happen. However, as you can see, there are lots of opportunities for "user error", too.