But you are arguing that needing 25 dex to wear a vest is somehow less arbitrary than only being able to hold 4 potions at once.
It is. Dexterity, stamina, and skill are more important than strength when it comes to a greatsword. At best, strength should determine your maximum, non-critical damage. DA uses strength though because strength is the warrior stat, not dex.
Moreover, it's not that you can't use a greatsword effectively with low strength, it's that you can't even pick one up and attempt to use it at all.
And all of that proves the arbitrary nature of attributes... how? Regardless of exactly which attribute should determine what, you seem to recognize that they are a clear and useful method of measuring human ability. Thus, they are logical descriptors, and a reasonable way to place limitations on the effective use of equipment. When I say, "I didn't design it," and follow up with specific examples of how to make the system more complex, that should make it clear that I am suggesting that the implementation could have been improved. It doesn't mean that I think the entire philosophy behind attributes is bogus. "25 dex" means something because it is a concrete value that fits within the game rules. It could be 2500 dex, so long as the scale is shifted accordingly. It's not a random number, and just like any unit of measurement in the real world, it makes sense within the context of the game's setting.
On the other hand, a loot system that allows me to carry multiple greatswords, broadswords, plate armors, books, plot items, and crafting components, but limits the amount of potions I can carry is, in fact, based upon an arbitrary restriction. It's not based on weight, it's not based on backpack space, and I do not have the option of choosing to carry more potions instead of some other item. It's strictly a game mechanic meant to limit my ability to use potions, and has no logical justification. Thus, it is arbitrary.