Why not, they both have stellar records in the subcontinent. Whether you rate them overall or not, it doesnt make a difference IMO. They both bowled with the kind of style that has generally achieved the most success in the subcontinent - i.e. give the ball some air, vary your pace and let the pitch do whatever it does instead of experimenting. Croft and Such were arguably the best spinners in all of England, far better than Giles. Unfortunately, Such couldnt hold a candle to Giles' batting ability while Croft was strongly disliked by the selectors.
I'll take your word for it. As I said, I cant be arsed talking about Giles and Croft. In any case, neither Giles or Croft were stellar in the subcontinent, as you say. Merely good (and certainly better than their overall career) and, for that matter, Croft never played in India or Pakistan, just Sri Lanka.
I think this Indian side is overrated in their ability for playing spin. I think it was different in the 90s when you had the likes of Sidhu, Azharuddin, Tendulkar etc who were as good as it gets against spin.Sidhu used to eat spinners for breakfast, lunch and dinner really. The likes of Kambli and Jadeja were not too far behind against spin either.
In the current side, only Tendulkar and Sehwag are really good against spin. Gambhir is still an unknown IMO. Laxman, Dravid, Ganguly, Yuvraj are all average players of spin at best.
You only have to look at the number of spinners who have had one off successes in India. Boje, Udal, Krejza, Clarke and even Swann had some success.
Yes, Sidhu was a monster. I watched a good number of Murali's matches against India in the 90s and Sidhu used to take him apart regularly. If I recall correctly, Murali said that he decided to revise the length he was bowling after having been smashed by Sidhu yet again in the 97 (or 98) tour of India. He felt that he was bowling too full and allowing batsmen too much of an opportunity to tonk runs against him. Right after that he started to become a lot more successful - his successful development of a good top spinner at the same also helped. You are right, however, that the 90s side were better players of spin than the current crop.
Strangely though, I would also say that the Sri Lanka side of the 90s were better players of spin than the current mob. Of the Indian side I would agree that Sehwag and Tendulkar are the best players of spin, but I would put Gambhir there as well. He is pretty good imo. Also, I would hesitate to suggest that Laxman, Dravid, and Ganguly are average at best players of spin, more that they are competent, if not in the same league as a Sehwag or Tendulkar. Yuvraj however is a poor player of spin.
I am not sure what you imply by your last comment about one off successes. As far as I know, all those successes happened on pitches favourable to spin, and as you note in your comments about Giles and Croft, all they would have to do was bowl "with the kind of style that has generally achieved the most success in the subcontinent - i.e. give the ball some air, vary your pace and let the pitch do whatever it does instead of experimenting." I dont see how succumbing to these bowlers in good conditions makes them much poorer players of spin than their predecessors (especially if you tie in the fact that they may not have taken these secondary bowlers seriously).