Nope, I've actually tested it multiple times. Shield Oath doesn't do what you think it does, and Sword Oath will always generate more enmity. Last night I did an informal test. I was in a party with another paladin and we were doing the final step in the DD chain with the single boss. The other PLD was 46 and I was 48, but we were both in shield stance and the other tank had a slight lead on me (maybe 3-5%, just a sliver) which I could not close. This is despite using Fight or Flight, and Spirits within on cooldown, along with the full Rage of Halone combo (did 5 halone combos without catching up). So I'm going to assume the other PLD wasn't screwing something up. (The reason I was behind was probably because I'm using a lvl 41 weapon at level 48).
So I went through 5 Halone combos, and I just kept falling further and further behind. So I decided to see what would happen if I swapped to Sword Oath. Within 3 Halone combos I was at the top and tanking the boss. I may have gotten a Spirits Within in there but that's neither here nor there. The other PLD didn't stop tanking the boss, I could clearly see them and their enmity didn't just fall off, each halone combo only put me a sliver closer and it only took 3 to close the gap.
This is pretty much anecdotal "Testing" but I've been in situations like this several times, this was just the first time it was PLD vs PLD. And every time it ends with the Sword Oath Paladin pulling.
Moral of the story: Shield Oath does not work the way you think it does and Sword Oath generates more enmity than being in shield oath. It makes sense, too. If you look at Enmity per global it's more than a 2% increase. It works out to ~54 enmity-potency per global. While Auto Attacks are 83, and Halone combo is 683. (Circle and Spirits are close to 25 each, you know this). so you have 816 baseline, and 870 in Sword Oath. That's a ~6.7% increase, which is noticeable.