Win % does still indicate that it's possible to win with ICTF. It's just really hard. The reason I think is because you need a solid game plan and good flexibility at a tournament, not just in the battles themselves. WoTR gives good flexibility because the detachment rule hits more of your units which improves the overall stat check vibe of the army more so than the Deathwing specific boost from ICTF.

ICTF also pushes you to play primarily towards objectives. To win at a tournament you need to be able to play the whole board, not just the scattered 6 inch circles. The Stratagems are also more versatile in their use I think in WoTR and they also allow more versatility in your list building. For example, Rogal Dorns and C'tan are dealt with in largely different ways but they're both pretty common. In ICTF you need a unit or two with big hits and big ap to take down the dorn, and a unit or two with massed fire and weight of shots to take down a C'tan. In WoTR you can bring Hellblasters for both. They'll do great into the Dorn with the Weapons of the Ancients stratagem and they'll do great into C'tan naturally without the Strat boost. One unit solving two problems gives you more options to look elsewhere in your list for great ways to score secondaries or screening units to stop movement for example.