I don’t like trap bar deadlifts as much as traditional or sumo deadlifts just because…hey…that’s the way I like to do them. I competed at the deadlift, so that’s what is fun for me. Even in odd lift meets I’ve never contested a trap bar deadlift.
In terms of strength training for cycling I would pick neither! Except in some very specific circumstances where cyclists were going to be doing very low rpm high torque in competition…think standing start track sprints, for instance. Otherwise I think there are other exercises that provide similar benefit with much less risk of injury. And I would opt for more bilateral exercise selection.
Strength training improves cycling performance in a few different ways…not all related to how many pounds you can lift off the floor. Muscle elasticity (just reducing hysteresis loss) and fiber recruitment improvements can increase cycling performance without a big concomitant increase in the weight lifted. For sure, moving a bigger weight in the deadlift can improve some aspects of cycling…but one thing that analyzing orthogonal strain gauge array power meters has taught me: it doesn’t take many pounds of force at the end of a ~7 inch lever (your crank arm) to generate triple digit increases in Watts output. If you can jam 5 more pounds on the end of a pedal you’re going to be overjoyed at the resulting power increase. Even 2.5lbs will make you super excited.
So the injury risk associated with deadlifting 50lbs more is just not worth it, IMO. Think of your ftp as a five thousand five hundred rep max. How well does that translate to deadlifting?