It's an interesting point you make there. But how would you differentiate not having clear cut opposition to simply being miles better than everyone else? You yourself say that even Marcus Gronholm wasn't able to defeat him.
Even though you say that Petter showed promise in 2003, he won the title because Sebastian had been ordered to ease off the throttle, coupled with Citroen's mistake of not giving Sebastian enough fuel in Turkey.
I find it impossible to compare different eras so I can't answer even begin to fathom how Sebastian would compare to the drivers of the 90s in their prime. I know it is semi rhetorical but I can't help but mention it 
In my opinion, Gronholm isn't the driver that Leob is. Its a weird situation for me to judge. Yes Leob derserve all of his titles but I just look at the current Rally field and there isn't anyone in a position to challenge Leob.
Citroen - even when they took a "sabatical" were always very strong. And as I've mentioned at Ford, despite Ford having the upper hand at certain events, their driver line up will take time to evolve.
Other than that there has been no real challenge to Leob

I Know its hard to judge in comparison with the past, but I can see Leob leaving the sport before anyone emerges as a potential rival
