How long was each Calm ?

[Christmas]

According to GAMEFAQ, the FFX and FFX2 Ultimania guides post only 5 "Calm" periods (below), with High Summoners appearing in intervals of 600 years thru 90 years. Now, here is my problem with it:
- We see that Yu Yevon takes only 9 years to rebuild Sin, as it was all it took for Sin to reappear after Braska defeated it.

- Does this means Sin is "alive" and loose around Spira for centuries ?
IMHO that is impossible. If Sin kills as we see it doing in FFX every single year during those large periods, the planet's population would be extinct after a while, say, 200 years

How long are you going to let the destruction continue?
Kefka: I've tapped into the ultimate power. Observe...!
Kefka: Such magnificent power! You are like insects to me!
Kefka: I will exterminate everyone, and everything!
People will keep rebuilding the things you take from them!
Kefka: Then I'll destroy those too. Why do people rebuild things they know are going to be destroyed? Why do people cling to life when they know they can't live forever? Think how meaningless each of your lives is!

It's not the net result of one's life that's important! It's the day-to-day
concerns, the personal victories, and the celebration of life... and love!
It's enough if people are able to experience the joy that each day can bring!

Kefka: I will destroy everything... I will create a monument to non-existence!
Life will go on! There will always be people, and dreams!

- Did Yu Yevon take much longer to rebuild Sin initially ? i.e. did he take, say, 500 years to create the second Sin ?
IMHO that is impossible. A threat that has not reappeared for a generation or two would not command such fear and devotion from people. Bevelle and Yevon's Church would lose a lot of it's prestige and influence after 100 - 150 years without Sin. The more "costly" tenets of the Church would be abandoned, i.e, Summoner training would be abandoned and so would be the machina prohibition

As proof I submit the Catholic Church. Sure we still have people who believe Jesus will come back, even after 2,000 years of wait, but the power of the Church to run our daily life has been gone for a long time. There are very few people who still refrain from eating meat on Fridays and even less people who abide by all the other tenets in the Bible.
There is no way people in Spira would still refrain from using machina after 200 years of no Sin!!!

So what gives ?

[/INDENT]

That will depends on how strong the leaders of the Church is. Especially when they rule with an iron grip. Besides, a lot of Muslim still observes their religious practices passed down from long ago.

The influence of the Yevon Church still remains after FF X which show that even without Sin, the Yevon Church still lives on inside the people's heart.