I feel a little silly jumping in on you guys conversation after it’s gone this long, but the Gilgamesh point you mentioned I really like. A lot of people play up Gilgamesh, and while it’s true that barraging an infinite number of mystery endowed blades at someone can normally solve a fight, that tactic is very primitive when it comes to warfare. Someone mentioned before that Instinct A granted the ability to dodge projectiles even up to firearms which is evident when Artoria dodges smg rapid fire from Lancelot in Zero. I don’t think it so unreasonable that she could use that to close the gap between her and Gilgamesh during a fight there. Combine that with the fact that she’s significantly better at swordplay than him and has lead many more battles and I could see his normal GoB tactics going out the window.

As for Ea, well you pretty much covered it. Ea isn’t really a weapon that’s meant to kill things like Excalibur is. It destroys worlds, but it doesn’t target people. That’s why Gilgamesh uses it to rip a hole under Iskandar’s Reality Marble and drop his homies in to it, as opposed to glassing his soldiers. Ea was created at the advent of the Universe (or Galaxy. Can’t remember which one), and displays more of like a terraforming/world managing behavior as opposed to possessing the intent to kill. That’s reflected in its a design as being more of a wand than a sword. Excalibur on the other hand is specifically forged to destroy people and things, seeing as to how it was created in the planet after the death of Ares to slay Sefar (Umbral Star Altera’s Route).

So when we break it down to concepts and power levels, Ea is a one trick pony like Gilgamesh that has the purpose of destroying worlds, and while destroying the world would kill the things on it, that effect is irrelevant if it’s used on a person. At that point you’re just a blanket level of force striking a point in front of you.

Excalibur on the other hand is made to fight people and things, and so it stands to reason that its power and concepts are more streamlined for defeating an opponent in battle directly. Gilgamesh technically misused Ea by shooting it at Artoria in their fight at Ryuudou temple, as you said, but also Excalibur benefits from being farther way from the opponent when the beam is fired (Hollow Ataraxia) so Artoria also technically misused it and only barely lost combined with the fact not all of the seals were broken. I could even argue that Gilgamesh with the intent on destroying the planet with Ea could justify the unlock of the seals too.

Also I don’t really factor Avalon in to Artoria’s strength since it’s atypical for her to have it. I don’t think there’s a version of her that can be summoned with it in her possession since it was lost before her death. She just so happened to reunite with it in that one circumstance, and it possessed every concept necessary to nullify Ea so. If we’re only looking at the Fate Route fight, then I think it’s okay to consider it, but otherwise it would be unreasonable to assume she has it in any theoretical matchup we put her in as a servant. Not to mention that fight as a whole is outdated seeing as to how Artoria and Gilgamesh both have been expanded on quite a bit since the original VN’s release.