The bold is exactly the point , Rasengan needs to grind into the tartget while Kaiten would repel it and its Chakra on impact. A Odam rasengan or two woulde likely push back the juubies tail , but it would first grind into it before sending it flying as thats the way it works , while Kaiten would simply repel it instantly with no grind time or lag.The Rasengan's very effect is to push someone back after grinding their way through one vitals with its rotation. We have two pushing forces clashing against one another, a Rasengan big enough would push back the Juubi's hand just as easily as a Kaiten, I don't see why you're putting one above the other to this degree as if there would be no contest when they make contact, especially when the Rasengan is empowered by Senjutsu.
Rasengan is also a rotional technique , but it grinds into the target by spinning in mutltiple directions before blasting the target away , so if it makes contact with Large Kaiten , its gonna get repelled instantly with no grind time or build-up since not only does kaiten repel physical attacks instantly but also Chakra itself , and rasengan is a ball of Naruto's Raw Chakra.
That Damage to the ground would not happen the way ur expecting since the Rasengan would get repelled instantly and sent away , so how can it grow if it repelled pre-maturely?And the thing about its landscape destruction here is:
It preceeds the explosion itself by a lot. The impact is what causes it primarily, not the explosion that follows. It serves to increase it, yes, but you can see it happening before the bright white light covers everything. Meanining it could still grow quite a bit before the explosion is negated by the Kaiten.