Hope this doesn't sound too primitive, but:
A torque converter is a necessary evil in some applications. For drag racing, it keeps your engine in the powerband at all times. For street, it allows you to drive without using a clutch.
But a torque converter is "lossy". It consumes HP doing it's job. Even a locking torque converter uses HP, but not as much.
For LSR, we have too much power at low speeds so staying in the powerband isn't necessary. Now, if you were running on asphault, such as the Texas Mile where you could actually use maximum power the whole time, it might be a good thing. But even then, a good driver with a manual will probably have the advantage at the same power level.