Did THF get DWII? I remember reading something about it, but don't see it anywhere online right now.
Anyway, even if they did that's still 10% difference. And that is massive, /WAR won't come near that bonus, not with Berserk and Double Attack and Aggressor. Why? Because I'm being realistic. You never have BRD/WHM and DNC with you in a party. I almost never have either.
THF/NIN with Suppanomimi, Raider's Boomerang and Nusku's Sash (max Dual Wield, except Auric Dagger) still needs 67% Haste to cap. With 25% from gear that still requires 42% magical Haste. That means you still need a BRD/WHM with Langeleik and +2 hands to get to cap. If you have that, good for you. Now your THF/NIN is almost perfect. THF/WAR swings almsot 20% slower now. Means when THF/NIN does 5 hits, THF/WAR does 4 hits. Double Attack gives you up to 8.4% extra hits outside of Abyssea and up to 6.9% extra hits inside Abyssea due to Apocalypse Atma (assuming you have no Double Attack gear, if you do the difference is even smaller). Effectively it means that THF/NIN still lands 17.5% more hits than THF/WAR (at least) in the same time. Do you think Berserk gives you 17.5% more damage? (Hint: no)
Oh, and Dual Wield, if not over cap, gives more TP than you lose for any relevant value in a time interval. I don't even know if it still reduces TP gain after cap, depends if it's applied before or after Haste. Anyone know which it is?
Saying THF/WAR can cap haste now is true but misleading. It won't happen in any amount to be relevant for comparison between the two subjob choices. Regardless, I wouldn't sub WAR on THF other than to post spike damage WS screenshots, which I'm sure plenty of people are doing. And regardless of that, even under the best of circumstances the difference is marginal at best. Hence, THF still got nothing. The only thing native Dual Wield is good for is so it doesn't unequip my offhand weapon when I change to /BLM for warp when I'm doing quests or something. Although I wouldn't be surprised if SE actually used that as an excuse why they're not giving THF anything else.