No, thanks. You know as well, picking up 5 copies with 28% variance is in no way representative for batches of hundreds or thousands of lenses. And you know as well, one can come close to perfection at reasonable costs, but getting the last 5% to 100% always super and maximum quality will make the product extremely expensive. I don't demand what I can't afford to pay for.
Other decenterred lenses are not necessarily telling me, my copy will also be one.
Other not-decenterred lenses are not guaranteeing me to get a perfect one. If it happens, I'll send it in.
If Sigma's facing a worse "good copy rate" than Canon, it would be soon enough to make it my problem after one of my four lenses turns out to be a lemon. 6, if one counts the fixed lens ind front of the Merills.
I tested and re-tested a lot of things, but decenterring is nothing I was looking so, simply for the reason, I don't photograph even brick walls and there are other, bigger problems involved if a picture with focus point off centre is not in focus. I don't think about decenterring but I do think about too much seeking a perfect lens can spoil a lot of fun. I'm only talking for myself here.
But here's a link which puts things a bit more into proportions: http://www.lensrentals.com/blog/2013/11/...-spec-lens
As I understood, in short words: Service is not always able to change a bad (decenterred, i.e.) lens into a good one, but sometimes to exchange my copy against another one.
I experienced that with Tamron. Sent it in twice, after that the camera bodies. Problems were not solved. They exchanged the body against a "new" one which had 1174 shots on it's counter when it arrived. I had some funny experiences with service and also very good experiences (Yashica, Zeiss, Mamiya, Pentax, Nikon, Sigma). And seeking for problems will nearly always succeed.
Assembly lines with robots - why not, for boring, repeating work? It's a fact humans get bored and the failure rate can increase. Our brain is not made to repeat the same grips all-day, week in, week out. To produce low-cost lenses in huge quantity and even quality, what would be your suggestions to keep costs down? On the other hand, robots are set-up, adjusted, maintained and controlled by humans, they will never produce better quality than they are set up to, usually they are not improving their workflow with experience. Learning robots are slower than their stupid mind machine colleagues.
By adjusting only one lens, there are so many variables, I'm still amazed how good they actually are. The first Zeiss Microscope lenses were made by try and error...
At least - who of us working always 100% free of failures? To me, that'd be a revolutionary experience. Evolution, by the way, uses very often "failures" and mistakes to create a better version of a living organism. It's not a "no, never!" principle. That makes it easier to deal with my own failures and also, to tolerate others.
5 copies with variance? So what? 5000 copies with no complaints, because there was nobody to recognize their flaws. And no one who kept track of statistics - even statistics can have mistakes ^_^