No it isn't, he is defeated by Numenorian forces before that in the source material. But for some reason Tolkien doesn't explain well Sauron is captured without the Ring. He then persuades the Numenorians to attack heaven, with predictable results, returns to Middle Earth, sets himself up again, is defeated by the Last Alliance of Elves and Men (not just Numenorians), and then the ring is cut from his hand.
I don't think it completely undermines it, nor is the ring all powerful. It's got the majority of Sauron's power worked into it, sure, but neither Morgoth nor Sauron were ever completely invulnerable to personal might. But the impression in the appendices is that the might of the Númenorians was SO overwhelming when they went after him his forces honestly routed from the field. He may have foreseen an opportunity to prey on Númenorian pride and fear of death when he begged pardon and that may be why he too didn't flee?
This is the kind of thing that wouldn't work well in TV. How do you show that power? Unless you are going to take the high magic approach and give them an army of fireball throwing wizards, you are limited to conventional pseudo-medieval military might. Which would not plausibly have a chance against the magical power of the One Ring as depicted in the movie. Remember, TV doesn't do subtle magic.
I don't remember anything from The Silmarillion. Too long ago and too boring a read.
One of the dominant themes of the Lord of the Rings was the diminishing of mortals. The people of the Third Age were lesser than those of the Second Age, who were themselves lesser than those of the First. Moreover, the Numenoreans had received great blessings and gifts from the Valar, most of which were withdrawn with Numenor's downfall.
In the books it's Ar-Pharazon that led the Numenoreans to sail against Aman. In this show Pharazon is chancellor. I wouldn't put it past the writers to have Chancellor Palpatine, I mean Pharazon be Sauron in this show.
The Numenoreans had gifts(enhanced life, strength, technology, etc.) from the Valar, plus the gifts of blood they got from having elven and maia blood in their veins. They were mighty enough and had great enough numbers that they could have destroyed him and all of his orcs, so Sauron surrendered and went to work from within to poison and ultimately destroy them.
On the death of King Tar-Palantir, his daughter Tar-Miriel was to succeed to the throne, but Pharazon forced her into marriage and claimed it for himself.
We know from the books that he wasn't invincible with it and he would surely know that. There's no way that he would take it with him when as a prisoner he would be searched thoroughly before he would be imprisoned on Numenor. Plus he would know that if he hid it so that it could not be found, he would be able to use it to reform himself should he be killed. Given the circumstances, it was very likely that he would have willingly been parted from the ring.
