Just a reminder that this Indian team's home dominance is comparable to ATG teams, so the fact that they're only as good/**** as everyone else away from home doesn't mean they don't deserve the No. 1 ranking.
Thrashed in SA and UAE but will be no. 1 if they can win one home series? makes sense
What's problematic about the ICC ranking system isn't that they don't make any difference between away or home matches. While I do think away wins are harder and hence deserve more points, this criteria does not actually offer any team advantage over another because it applies to all teams.
What's problematic about the rankings is what's problematic about world cricket as a whole - the greater power that Big 3 teams and boards have which allows them to shape world cricket in a way that favours them. Australia, India and England play each other almost every 1-2 years in big 4-5 match series, plus they also get the heaviest home schedules of at least 5-6 Test matches per year. India had 13 Test matches in their 2016-17 home season. It's a fair question to ask how many teams in the world would get a home season like that and would India have gained the buffer at the top they did without that home season?
Before anyone misunderstands me, this isn't to say India don't deserve the number 1 ranking and they didn't have to play great cricket over that period to win those series. All those things a just as true for India as any other team - you have to win test match after test match to become a number 1 team. But there are a lot of teams who barely play 4 test matches a year, and that's what puts them at a disadvantage in earning points when competing with someone who plays 13 test matches at home.
So that's why you have a situation where Australia have had a pretty terrible year in Test cricket yet just one home series win against India will take them within the top 3 rankings. Same with England - got hammered in Australia, drew at home against Pakistan, but one series win against India at home and can easily make up for all the series lost.
Other teams who don't get to play as much or as regularly against these teams, never get that opportunity.
The schedules are geared in a way that India, Australia and England will always be within the top 3-4 ranked teams in the world over a period of time.