You on the other hand keep insisting that arunachal is the focal point where the river starts and therefore its being grabbed by china.

Never said this, come up with more interesting headcanon

No ones genuinely buys that siang just pops out arunachal.

Again, never said this. the point is that losing control of 90% of your water supply is a lot worse than the current situation of not controlling 10% of it. Numbers!