Lens technology has come of age, just like many other technologies - whilst we can coo about sharpness in the corners, contrast, AF performance, the 95th percentile of us "experts" can't honestly see the difference, just in the same high end audiophile equipment - there's not a great deal of difference for the 99th percentile of us between equipment costing £500 and £50,000.
What still has room for improvement though is dragging the bottom end up in terms of quality for price, not just the optics, but mechanical quality, physical construction, AF performance etc etc etc. Similarly with the cameras, it's about dragging the low end up, the entry level camera now is beyond what the 1D was a decade ago, the entry level camera in decade will be very close to what we have in the 1Dx and 5SR today, subject of course to marketing people ;-)
There is very little difference between the players, just like cars today, you can't really get a bad or even average DSLR or MILC if you tried, all the lenses are outstanding, it's just us as humans wanting something to differentiate us from the pack - some of my favourite photos were taken on what I'd consider to be poor cameras, my best musical moments have probably been listening to an MP3 in the car, my greatest roadtrips were not in my most expensive car.... Which computer do we remember with greatest fondness ? Probably a Commadore 64, Amiga 500 or that old i486 !
Zeiss Otus ? Yep, they might excel in areas, but £4000 compared to the £100 Canon 50mm ? Is the former actually 40x better or just quantifiably about 3x better ? There's a curve of deminishing return used extensively in hi-fi equipment, I've seen it used more in computers and I've used it for a couple of decades in my work as a civil engineer designing road systems - 100% costs many times more than 99%, sometimes the best value for money comes at the point where costs just start to ramp up, before the silly money - who determines that point ? You do ! What is value for you, may well be very different for Joe next door.