LotR, Book VI, Ch-1: The Tower of Cirith Ungol

[Butterbeer]

Shame on you Gor, CAB and Landroval ...

... what is this 'agreement' notion that you speaketh of?

Considering that even if Gandalf had mastered the ring, there would be a delicate balance between the ringed-Gandalf and ringless-Sauron, I would say that Sauron has retained more power than there is in the ring.

Actually, i DO disagree with this. I don't think this is actually relevant here: I see it not as a simple mathematical sum,

Gandalf's power plus the One Ring's power versus Sauron's power



The point is here, no one doubts as and when gandlaf finally masters the ring and focuses his will into getting the full power and command fromj himself and the ring, that he would defeat Sauron with all his rings, and armies and fortresses / allies etc ...

the point from your quote relates more to the time and effort it would take gandalf to become the Ringlord and Lord of the rings, whilst sauron would have a window of opportunity with his armies and allies to attempt to defeat gandalf in this time.

Thus i think it bears little to no relevance to the Ring V's sauron.

... saying that Sauron put the greater part of his power into the Ring.

Yes, this is what i refer to: and indeed for the whole history of Middle Earth and the rings of power to make any sense it must be so!

Else why, when the ring is severed from him does Sauron flee, a disembodied fea?

Why when the ring is personally delivered into the fire by Gollum and Co the toothy couriers ... does the foundations of baradur (built with the power of the ring) and Sauron vanish in a twinkle of a hobbit lasses's eye?