If two 5fers in England is enough to make Yasir better than Ashwin career haul of 26fers and dominance in Asia, then by that logic Sehwag is the better than any Pakistani batsman ever because he has produced 3-4 centuries in SENA and has bosses Asia more than any other batsman ever.
You've nearly hit the nail on it's head. But just missed the point. The question is how many of Sehwag's SENA centuries resulted in Test Wins? Because it's not just about the number of times you clock centuries overseas, it's about their impact. If Sehwag's 3-4 SENA centuries resulted in wins, then by all means he should be near the top. Inzamam rated Sehwag extremely highly because he was a match winner. He said that he would take an 80 that resulted in a win, over a 500 that resulted in a draw any day of the week.
That's reason Saeed Anwar is held in such high regard in Pakistan is because 6 out of his 7 overseas centuries resulted in Test wins, including wins in South Africa, England and New Zealand. That's an insane win rate. And the same holds true for bowlers
Fact is if we had Ashwin in Lords or the Oval in 2016, or for that matter any other spinner, in all likelihood we would have lost the game, or at best drawn it. Yasir was the difference. And that ability matters.
In the UAE we were whitewashing teams with Zulfiqar Babar and Abdul Rehman, hardly world beaters, but excellent in home conditions. Quality spinners at home are very handy, and there is absolutely no doubt that Ashwin is the best of those. But the really great spinners, well, they will win you games where others wouldn't.
I will grant you though that Leg Spinners have a natural advantage overseas, at least that's what the statistics suggest. The effervescent Mushi took a number of overseas five fors in wins in Australia, England, and New Zealand. Qadir had a fair bit of success too. As i'm sure kumble has too. But the really great finger spinners of recent years, the likes of Murli, Saqlain, Ajmal have all had five fors abroad, albeit in less successful tests. Murli of course has winning ones of course but he was the greatest of them all.
I still believe in Ashwin's ability. I think he may be a victim of his own success at home. Too much is expected of him overseas. But he does a decent job, contributing as best he can. He just needs those wins. Those critical wins. Even if he gets a three for or something.