Seems like everyone is reciting from the same script so instead of quoting everyone and repeating myself, I will just add my two cents here and address most of the points from my perspective.
Yasir did well in England, was good in two matches and dreadful in two, but he was completely exposed in Australia and that is what I feared when he was running through teams in UAE and Sri Lanka. It is normal for a spinner to not take wickets when there is no assistance, but he got smashed like no tomorrow - he got the Imran Tahir treatment.
The sign of a top quality spinner is his ability to bowl both aggressively and defensively, and Yasir is clueless when it comes to the latter. He looks great when his tail is up and he is taking wickets, but he turns into a kitten when the batsmen take him on. He simply cannot contain, which is a big problem, and puts extra pressure on the other bowlers because it allows the batsmen to settle. However, when you bowl tight spells, you don't allow the batsmen to settle and other bowlers can capitalize. Ashwin though, can do both. He is both aggressive and defensive, which means that even when he is not taking wickets, he doesn't get smashed.
It is true that Ashwin doesn't have any match-winning performances overseas yet, but he will get another shot in England soon. However, he has outperformed Yasir everywhere else where both have played, and now Yasir will get a chance to match him in the WI. Yasir was ahead of Ashwin before the Australian tour, but that is where the wheels came off. Let alone Ashwin, he is not even better than Jadeja. It is time we stop thumping our chests after the way he got exposed in Australia.
All this talk of Ashwin getting out-bowled by Lyon and O'Keefe etc. does not mean much. In the UAE, Bishoo matched Yasir blow for blow, and he was supposedly bowling to the 'best spin playing team in the world', a myth that is peddled around on PP, even though I have lost count of the number of spinners who have pulled the rug underneath our feet in the last few years. Not to mention this whole talk of Ashwin getting dropped in SA is pointless as well, when Yasir himself got chopped in NZ. I am not interested in the excuse that it was a tactical change. The fact is that the management did not have faith in him bowling economically, and thus dropped him.
Nonetheless, I'm simply flogging a dead horse here. It is a proven fact that Pakistani fans are the most delusional in the world. Almost every Pakistani player is better than their Indian counterpart in their opinion but somehow, India continues to outperform Pakistan in all formats. Enough of the fluke 2-2 series in England, where we played in late summer and got dry pitches, and England had a unsettled top-order of Hales, Vince and Ballance, while Anderson and Stokes were nursing injuries. Anderson was below his best because of his shoulder injury prior to the first Test, and Stokes only played 1 match. Anderson was in imperious form vs SL but his pace and swing was down vs Pakistan, and it is not just the conditions because if Woakes could swing the ball, so could Anderson. However, he wasn't at his best. It was a one-off performance and India have outperformed us on their overseas tours apart from that, so it simply shows that India is a better Test team than Pakistan, which is also true when you compare them man to man.
That is all I have to say on this issue. Now I will let some folks continue to live in a parallel world where the overweight Shah is better than Ashwin.