So what you're telling Canon is that you prefer features despite the poorer QC. And they're listening. Tell Canon with your purchases that you value QC over features and I suspect that's what they'll provide. Or provide both - but be prepared to pay more.
This is sounding like an opportunity! How many would be willing to pay for a cherry-picking service? Suppose an enterprising individual were to buy a dozen samples of a lens, test them all, and return all but the best. Would you be willing to pay this person to do the QC the camera makers have skimped on?
Exactly! A lower quality lens with the right features is often preferrable to a first class lens without the features or with the wrong features.
A medium quality 150mm lens in a zoom will likely provide more satisfying results than the best 100mm prime ever made, if the FoV of the composition is that of a 150mm lens, making it necessary to crop the 100mm shot.
Likewise, a hand-held shot at the long end of a 100-400 medium quality zoom with the feature of IS, using say 1/200th sec exposure at ISO 200, will likely provide better results than a Zeiss 400mm prime without IS, at the same shutter speed and ISO.
Features can be important, particularly IS and accurate autofocus. I think Canon have demonstrated they are capable of manufacturing a lens with the IS feature without compromising the optical MTF response. For example, the 70-200/F4 IS is at least as good, and slightly better I believe, than the highly acclaimed previous non-IS version. Also, the recent 100/2.8 IS seems to be optically as excellent as the previous non-IS version, if not better.
I don't think an ad hoc cherry-picking service as a business would be allowed. There would be legal ramifications. What would happen to the returned lenses? It would be fraudulent to sell them without mentioning they are the rejects of cherry-picking.
Of course, in an informal manner, this is effectively what has been occurring for years. I once went to a lot of trouble comparing the Canon 400/5.6 prime with my 100-400 IS zoom which is noticeably soft at F5.6. I understood the 400 prime was supposed to be at least as good at F5.6 as the 100-400 at F8, its sharpest aperture.
Although the prime lacked IS, being sharp at full aperture would give it an advantage in certain circumstances when the subject is moving and a fast shutter speed is required irrespective of an IS feature.
I was surprised to find that the copy of the 400 prime I'd bought was not even as good as my 100-400 zoom. It was the last one in the warehouse, apparently. After my testing, it was returned to the Canon agent (by the retailer) for adjustment and tweaking, and I then repeated the whole series of tests on the same lens. I detected a very marginal improvement as a result of the adjustments, but not enough to make it sharper than the zoom. I got a refund.
This seems clearly a case of a Grade C zoom being compared with a Grade E prime. Whoever subsequently bought and accepted that lens that I'd rejected, would probably not be aware it was a Grade E within the QC manufacturing parameters for that particular model.
I'm advocating a system of honesty and transparency whereby the entire output of lenses is subjected to a rigorous MTF testing procedure along the lines of the old Photodo tests.
The additional cost might be 10% of the wholesale price of each lens. Such additional cost would be borne by the purchasers of Grade A and Grade B lenses plus a small discount that rightfully should be applied to the Grade D and Grade E lenses. Grade C lenses would cost the same as usual.