Let's look at this: If you can wield weapons as if you were one size larger, and if we can agree that Oversized affects how you wield weapons (if we can't agree upon these then I'm afraid I have little intellectual respect for you in this particular case), then it can be argued that for the purposes of Oversized (which affects how you wield weapons), you can wield weapons as if you are one size larger than you are. Since you would actually be large, you would be treated as Huge for Oversized, and thus could wield Gargantuan weapons. That is my argument.
This is where the argument breaks down. You are large. Oversized allows you to wield large or huge weapons
because oversized keys off of your base size.You are large and wielding a huge weapon. Eternal Defender allows you to wield a huge weapon
because it keys off of your base size.Neither ability increases your base size and both of them reference a comparison to your size as the basis for the ability. It
could be read to mean that, but it would be wrong since both abilities clearly reference your base size as the basis for the increase. The wording is there and quite clear, I have made my point and you have made yours and I don't see that there is a whole lot more to discuss. If we disagree, we disagree, which is fine since we aren't gaming together
.
I also agree that the oversized argument has been done to death, you did put in your OP statements about it being removed as a bad thing... which kind of opens up that can of worms. Happy to drop it though, here's hoping you can find a DM who will let you play oversized, I think it would be fun even though I would feel bad for the other PC's.