I know Ashwin's record overseas is not the best but he has'nt been terrible since 2014 either. In fact, for all the hype, Harbhajan couldn't buy a wicket overseas. It took Kumble 2 full tours of Australia and England before he learned the art of taking wickets in Australia or England (he had terrible tours in 1992 and 1999). Murali had a terrible record in Australia as well. If you even followed India`s last tour to Australia, Ashwin bowled really well in the last test at Sydney and just did`nt have the support from the other end that test. He just played one test at the Oval in the 2014 England tour and bowled very well. I'm not a huge Ashwin fan but I`ve seen those tests and he looked like someone who could take wickets in those tests which is not something I would say about Bhajji in Eng/Aus or even Kumble pre-2003. Coming to this batch of overseas tours, he was good in the first innings at Centurion and took wickets in the Cape Town tests in the limited opportunities he had to bowl there. Again, he was really good in the first test at Birmingham in England and did a good job at Trent Bridge as well (was a seam dominated test again). The only let down was in the second dig at Centurion and the really vital second innings at Southampton in England. I don`t see why were are writing him off. Anyone who has seen test cricket in England and Australia would know that it takes overseas spinners a while to get used to these conditions. You would`nt write off Kumble or Murali's careers because a bulk of their wickets came in the SC, would you. Similarly, overseas spinners seldom do well on Asian tracks despite all the talks of you just having to turn up to take wickets in those conditions.
Ashwin`s averages in England and SA since 2014 are 30 and 32 which are not horrendous. This will be his final overseas tour if he fails to deliver in any case.