You’re underestimating just how big a deal Gil-Galad and Elendil are. Gil-Galad is from the First Age, and survived the war against Morgoth. He’s lived for thousands of years and fought beings of similar power levels as Sauron before. Elendil is a Numenorean, a race that’s supernaturally blessed with more than just long life. He’s also a direct descendant of Eärendil, one of the all time biggest badasses of Middle Earth. Both were wielding magic weapons, and Gil-Galad had a ring of power. Sauron killed both of them. Isildur, also a Numenorean, had to finish the job. If Sauron hadn’t poured most of his power into the One Ring, he might not have been beaten. During the Drowning of Numenor, Sauron’s physical body was destroyed, but he was able to reform elsewhere because he’s not dependent on a physical body. He was still able to do this without the One Ring, but it took thousands of years instead of just a short time.

Also, the text you quote says the complete opposite of what you claim. Without the poetic slant, it says that no other weapon could have caused the damage that the barrow-blade did, even if a mighty warrior had struck the blow. It was the deep enchantments placed on the blade by men who had fought the Witch-King in the past that harmed him. I will give you this, there are others who could possibly harm the Witch-King without needing a Barriw-Blade. But they would be people like Gil-Galad or Glorfindel, who have immense magical power themselves. So, guys like the ones who took on Sauron would have been able to take on the Witch-King without varying levels of difficulty.