Whether Kumble was the third best spinner of his era or not is debatable, but he is certainly not in the top tier. At best, he can be called the third best of his time, and if being the third best of his era makes him the third best of all time, that means no other era produced any great spinners.
You are just spouting an opinion, which is fine by itself. Kumble's numbers, in Test cricket, do make him a part of the top tier. Ask any cricketing expert, they will tell you exactly that. Ian Chappel called him "one of the greats," Ponting described him as "one of the modern-day greats."
And in Shane Warne's own words: "The best I played against? Mushtaq Ahmed was outstanding, but it has to be
Anil Kumble."
You said that Saqlain had a short-lived good run, but he averaged 15.84 in winning matches with 188 wickets in 93 games and 288 wickets in 163 ODIs overall. Those are elite numbers. Yes, he didn't have longevity of Murali but statiscally, he is far ahead of Kumble.
In ODIs, yes. In Tests, Saqlain took a third of Kumble's wickets before checking out. You are comparing a cricketer who took almost half of Kumble's career wickets (Tests + ODIs) to someone who ended up taking 956 international wickets!
Kumble's ODI average worsened in the latter half of his career, partly due to a significant shoulder injury sustained in 2001 that reduced his accuracy and potency. Prior to that, his ODI career included being the leading wicket-taker in the 1996 World Cup. His 6 for 12 against the West Indies is not only the best by any Indian bowler but also the best against West Indies.
You tried to project that Shane Warne was close to Anil Kumble, but with every filter you apply, Warne will still be ahead. And most importantly, Warne won Australia the semifinal where South Africa were 48-0 after seeing off the opening spell of Glenn McGrath. Warne changed the match within two overs. So he was not just dependent on McGrath for his success.
We are talking about career spans and you bring up one match! Moreover, Mcgrath is a much bigger ODI great compared to Warne, on every single bowling parameter. Which bowler was better than Kumble, in ODIs or Tests, while he was playing for India? Kumble took 30% of the wickets, in Test matches, when he was playing for India.
Our bowlers, historically, have not been as good as we made ourselves believe. They lagged behind their contemporaries.
The Indian Team itself lagged behind, and whatever they achieved in Test Cricket, during the late 90s to 2007, was thanks to Anil Kumble. He delivered 40,850 balls in his Test career, the second-highest by any bowler ever. He is only the 2nd bowler in the history of Test cricket to take 10 wickets in an innings. He ended up with 619 Test wickets, third highest among all spinners, again in the history of Test cricket.
He had 4 5fers and 1 10fer in Australia. Another 5fer in South Africa; 4fers in both England and NZ and 3 5fers in West Indies, when West Indies wasn't a minnow team.
Add to this the fact that the pitches he operated on weren't as spin-friendly as they are now. And the lack of DRS during his playing days, and we are talking completely out of context, with regards to his perceived greatness.
Ashwin has just retired in Test cricket and I don't want to list his achievements, which are many, and he certainly wasn't second to any of his contemporaries in Test Cricket.
This kind of blanket criticism, without context, is frankly quite reductive, if not juvenile. Anil Kumble lagged behind his contemporaries, namely Shane Warne and Muralidaran, because every spinner in the history of Test cricket lags behind them.
There is no spinner, at present, who is even remotely poised to come close to those two, or Kumble, for that matter.
Kumble is a national treasure and one of the all time great spinners in Test cricket. And, in ODIs, he would still make the top 10. Top 5, maybe.