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human
[LotR] Why was Sauron able to be defeated so easily?

I'm sorry if this has been asked before but I searched key words several times and didn't see it asked before.

1: I understand that the ring was severed from his finger but why would that just make him die then and there, and not have to be dealt a mortal blow afterwards since all of his power wasn't in the ring?

2: Why was the broken Narsil even able to do that, I realize it was a very well forged sword but should Sauron with all his magic and power be that weak to normal weapons? 

3: Did he not realize this could happen, if he lost the ring in battle he would just die, you'd think he'd try to protect his finger with magic or armor or something? 

4: Going by all of this, other than the controlling of the other rings and the corrupting of the nine kings of men into the Nazgul, would he have been better off not making the ring in the first place, as in: 

A: Would he have been defeated so easily when that battle eventually came? 

B: I realize the ring made him more powerful too, but how? If he just put his own power into it how does it make him more powerful rather than just at normal power when wearing it? 

C: I understand it has a some magical enchantments that enhance his powers in some ways, but why didn't he just make an enchanted ring that didn't just break up his power in a way that could be a major nuisance to him later (which it was)?

D: I always figured he did it to prevent himself from completely dying if he is defeated, (But did he really ever plan on losing in the first place?) but a lot of people seem to think he came back without any assistance from the ring, (since he never came in contact with it) and that he was powerful enough that he would be able to come back any way if he never made the ring in the first place.

Sorry this is so long. And (Sorry to break the fourth wall here) I don't dislike the Lord of the Rings at all so I'm not trying to be critical of Tolkien's writing style and story decisions at all, in fact I really enjoy it. I never finished the books because I was busy around the time I started reading them so I only finished The Hobbit and most of Fellowship (I've been meaning to read the rest but I don't own them) so I'm not sure if this comes up in the books but I've just been wondering about all this.
gpt
1. It wouldn't. Sauron was "killed" by Elendil and Gil-galad, but they died, so Isildur got to loot the corpse.
2. There are certain weaknesses the Ainur accept when they take physical form. One of these is the ability to be killed by physical attacks, which would include swords.
3. Cutting the Ring off his hand would not defeat him.

A. Yes, Elendil and Gil-galad would have still been able to kill him, and it's possible he would then have been too weak to ever come back.  
B. It wasn't primarily a combat bonus; it mainly increased his abilities to intimidate, dominate, and manipulate others' wills. He gained power from making the Ring in the same way a master blacksmith gains power from making a sword, i.e. tapping into his own crafting skill and untapped potential.  
C. In order for the Ring to do everything he wanted, he *had* to put tons of his power into it. Creating powerful things always requires a sacrifice in Middle-earth.  
D. It's unclear whether the Ring helped Sauron return after his "deaths", or whether he was powerful enough to return anyway. If so, that was really just a side effect. Sauron did not create the Ring with the intent of preserving himself after "death".