Just take the example of the West Indies, which became a really weak Test team at the turn of the century. From 2000-02, England comfortably beat the West Indies 3-1, Australia whitewashed them 5-0 and South Africa went past them 2-1. Then Sri Lanka whitewashed the Windies 3-0 followed by Pakistan 2-0 in a 2-match Test series. You will have to scratch your head to go back to such a top eight weak Test team.
After the above, the very next series played by West Indies with a top team was India at home in 2002. That team was led by Sourav Ganguly who had beaten Steve Waugh's mighty 'invincibles'. The Indian team also boasted of a really great batting line-up. Ganguly's India still lost to a 'weak' Windies 1-2 in a series we could have easily won.
When we visited the West Indies again in 2006 in a four match Test series, they were even weaker, yet the first three Tests ended in a draw. In the final Test, only a treacherous spinning pitch which would have made India proud (captain Brian Lara even gesticulated angrily at the groundsman while batting) and two brilliant half-centuries by captain Rahul Dravid (the highest innings was 219) saw us win the series.
As Dravid was basking in the glory of becoming only the second captain in 35 years, he was totally foxed by a reporter who asked him, "But shouldn't you have won 4-0?"
In 2011 too, we had almost won a Test series on South African soil, won the ODI World Cup and were No. 1 in Tests. When we visited Australia, a lot of commentators said that India was at its strongest and Australia was at its weakest.
We had our greatest captain and our greatest batting line-up ever and Australia had been beaten by both South Africa and England at home and lost a lot of senior players. That "weak" team not only won, but whitewashed us 4-0. That "strong" team not only got whitewashed, but did not even compete or look like getting close to drawing even a single Test.
The truth is that Test cricket is a different league altogether and any "weak" team can maximize their resources and shut you out with a draw if they can't win. Just recently in July 2016, Sri Lanka whitewashed Australia 3-0 at home. No team falls that fast no matter who retires.
Rangana Herath is probably still the best spinner in Sri Lankan conditions. Lakshan Sandakan got a 5-wicket haul in his last innings. Angelo Mathews is a solid batsman. Dimuth Karunaratne was among the runs. Kusal Mendis hit a century. This is an upcoming and rising team. We just made sure they didn’t rise "now"!
Another question! How many 3-0/4-0 Test whitewashes do we have outside India? The answer is zero. We couldn't achieve such feats even against Zimbabwe and Bangladesh in the past let alone other teams.
Great teams have to beat the really good teams and whitewash the really bad ones. Indian teams in the past would achieve the first but never come close to doing the second.
We have won three Tests in an overseas series just once in our history, the 3-1 in New Zealand way back in 1968. So you can see how the 3-0 in Sri Lanka is a big cause for celebration. This is also our eighth straight Test series win with five being in India, two in Sri Lanka and one in the West Indies.
We have never dominated the ICC rankings so much. The team is Number 1 by a mile. Sir Ravindra Jadeja is No. 1 in bowling and all-rounder rankings. Ravichandran Ashwin was No. 2 after the second Test. Cheteshwar Pujara and Virat Kohli were in the top 5 batsmen. It's a fine all-round team that is building up.
Sri Lanka is visiting India next and if we win that then it will be nine successive series wins. After that if we beat South Africa in South Africa, then Virat Kohli's team will rightly claim to be the greatest Indian Test team of all time, though that is still far off.