Well there are many better wicketkeepers than Dhoni. If you feel that he is the best we have currently then I feel sorry for you.
Name just 1.
And yes I the openers played a huge part. I'm taking about the time when India reached the number 1 spot. The only 3 guys who piled up runs were Sehwag, Gambhir and Sachin.
Dont look at that point in time itself. Its not like on November 15 these guys batted well, and on November 16 India was no.1 due to that.
It all started since way back in 2007 or so. And it was the whole team that played well, and not just the openers. If u can show me 10 innings from Sehwag or Gambhir, i can give u 10 innings where they failed & still India went on strong. Opening is important. But u dont win matches on the back of it. And then the run at no.1 lasted till around mid 2011. Gambhir was anyways out of form since he reached no.1 in start of 2010. He played badly against the visiting African team & he has slid down since then in Tests. Neither was Sehwag in that great a form. Still India stayed no.1 for 1.5 years.