I wonder if some of the apparently OCD behavior with questing for the perfect lens has to do with passionate photographers well out of their spending comfort zone.
Or are there really so many bad copies of great lenses?
My context, I am one of the people having had issues with the 24-70 II. I had eight ( 8 ) copies
that I returned. So, I have a little perspective on the sample variation of this "elite" lens.
Regarding the first part, I can only speak for myself and I was comfortable with the amount I spent. Matter of fact, I was ecstatic to be getting that lens for the $1,699 price (actually closer to $1,550 after all the different points, etc). But I wanted that lens to be in my kit has a main stay for years to come. So I did test it vigorously.
My tally was: 4 sent back for the "clicking" sound. Three were very loud, one slightly less so, but I did not need to hold it to my ear to hear the clicking on any of them. I contacted Canon, they advised I return the lens. But these returns were really out of fear of the unknown. Why is it clicking? What will happen in the future? Some people say the clicking goes away....but that sounds like either metal fatigue or wearing off small parts to me. Long term impacts? To me the clicking sounded like metal being compressed and released, like something was over torqued during assembly. Hard to tell, but people on the forum said it was atypical...canon said it was atypical. So 4 copies went back. I tested one of them optically, the first, and it was optically great. I didn't optically test the other three.
Copies 3 & 7. Both these copies were incredibly sharp at 24 mm, especially copy 7 (sharpest at 24 mm of all the lenses I tested). But they both had issues at 70 mm. In addition to being significantly softer than the other copies I optically tested at 70 mm, there was an odd AFMA issue where I had different AFMA values at different apertures. I still do not understand why and have been worried it was me, my camera, my tests, etc. But I did multiple tests using Focal, and the tests were pretty consistent. In addition, I lined up more real world tests for Copy 3 and I could see the center focal plane shift depending upon the aperture.
Copies 4 & 8 I almost kept. Copy 4 was probably the best copy. It wasn't the sharpest of the copies at any focal length, but it was close enough. More important it was consistently good. But it had a small bubble in the front element. Despite that, I did almost keep copy 4. I couldn't get the bubble to optically interfere with any shot that I took. The deciding factor for me was resale value. While I plan to keep this lens for years to come, plans change. And I know me, I would probably have been right up front and advertised that the lens had a bubble in the front element, likely killing my resale value, if I was to ever sell it. I thought about sending it to Canon to replace the front element, but that introduced a huge unknown factor for me.
Copy 8. I almost kept this one as well. But, by 8 copies, I was pretty sour on this wave of lenses coming from Canon. Copy 8 was pretty solid. It was actually better than Copy 4 at 24 mm and 70 mm from f 4 through f/11. Which was fantastic. But from f/2.8 to f/4 the IQ was noticeably worse. By noticeably, at 70 mm the Focal score was ~25% lower. At 24 mm the Focal score was ~15% lower. Worse yet, I printed off online copies of the ISO 12233 chart and I could see the difference in the center IQ. The edges were very comparable. Like I said, I almost kept this copy. But, through this testing, I have come to appreciate my 24-105 f/4 as I was always comparing the varies copies of the 24-70 II to it. My 24-105 f/4 actually seems to be a very good copy and had only slightly lower performance than the various 24-70 II copies from f/4 to f/11. So it got down to I am willing to spend the money for a 24-70 f/2.8 II that was sharp overall, but it needed to be sharp from f2.8-f4, because I already have sharp covered from f/4-f/11 with my 24-105. This was true for copy 1 (but it had clicking) or copy 4 (but it had a bubble in the front element), but not copy 8.
So all 8 copies have now gone back. So, was I OCD? I am an engineer. I am always a little OCD. But I would have happily settled for a reasonable copy of the 24-70 II. I tried two sources (amazon and adorama), had lenses made from Sept 12 through June 13, and had 8 copies that had at least 4 different types of issues. I am sure there are good copies of this lens out there. But my experience tells me that I should give Canon awhile to fix whatever issues they have going on before I try to buy this lens again.
BTW. I also jumped on the 70-200 f/2.8 II sale ($1,799, closer to $1,675 after all points). It isn't perfect, but it is good enough. I also tested several of my other lenses as I went through this process. They tested out fine. The 24-70 II is the only lens I have ever returned. And it just so happens I have returned it 8 times.
So my conclusion...to speak to your final question, unfortunately, IMO there are a number of bad copies of the 24-70 II out there right now.