All this chest beating claiming one lens is so much better than another or one mount is so much better than another is nothing more than fanboyism gone wild.
Some lenses are better than others, this is a fact of life. Whether that matters to this or that photographic application is a different story. I personally feel that the aspects that are most visible in final photographs are color purity (lack of CA), look of bokeh and micro contrast but other may have different preferences.
Whether I could identify with what lens a given image was taken is an interesting question. I may be able to for some lenses, not for others. Among my own lenses I am pretty much able to tell, but I may have vague memories of what I was using also, so it's hard to tell for sure.
Some eye AF systems work better than others and I personally think that this can make a difference, but also that anyone unable to make the AF of most current camera work for actual photographic applications is lacking skills. Yet, I don't call fanboys those claiming that there are differences... because I know there are differences.
The same applies to many other aspects of camera equipment: auto ISO, ergonomics, weather sealing, flash synchro speed, flash duration, quality of EVF,... and there are factual differences one way or another along all these dimensions. Some matter, some don't, some matter to some people, some to others.
Isn't the ultimate fanboyism the categorization of what matters and what doesn't based on the perceived strong points of one's own system?...
Cheers,
Bernard