Round 1: Pure h2h fight in an empty parking lot. No armor, fighters are in plain clothes.
Round 2: Fighters are in their latest armours. Diana has her sword and shield. Arthur has his trident. Fight takes place in a big swimming pool with only 3 inches of water.
Diana should take round 1 IMO. Arthur has more impressive piercing durability, but that's about the only area on land where he is better than her IMO.
Round 2 is closer. I'd still be inclined to back Diana, but she'd just have to be careful not to allow him time to do his water shield shenanigans, because it doesn't seem like he needs much water nearby to do it.
I assume the OP explicitly excluded the lasso because we've seen it affect Arthur in JL already (when he was sitting on it), so it might be too big of an advantage of Diana.
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