Okay...
Differences between trap bar deadlift and regular deadlift:
More knee flexion, less hip flexion.
Looks basically like a squat, but instead of bar resting on traps/delts it's beind held.
Effects: more quad recruitment, slightly less ham/glute recruitment, equal trap recruitment (weight is still held), less erector recruitment (you don't bend over as much).
B -- your theory that trap bar deadlift doesn't carry over is completely unfounded. Would you agree that a squat carries over to a deadlift? Because a trap bar deadlift is more similar to a regular deadlift than a squat is.
A trap deadlift is a squat/deadlift hybrid. Both are useful motions. Why is the trap deadlift, then, useless?
WSB, which a lot of you trap-deadlift-bashers perform or agree with, acknowledges how similar squat and deadlift are by lumping them together into "lower body" speed and maximal days.
So, please, a trap bar deadlift is just another tool, no better or worse than a regular deadlift, just different.