I think the U-Haul theory was still a valuable contribution, even though it was debunked thoroughly. It honestly tried to make sense of the facts known at the time. Adam's contributions to the case were considerable, even though he always insisted on Tom's contributions being more important.
It's a real horses / zebra kind of thing, though.
The situation: a hiker goes missing in an area where hikers are known to go missing (and, sadly, die).
The problem: eyewitnesses report the hiker's truck being in one direction, then not present at all, then in another direction.
Solution 1: eyewitnesses were mistaken about whether they saw the car / what direction it was facing
Solution 2: someone stole the car, took it away for a bit, and then returned it to the trailhead
Occam's razor requires only one additional assumption for solution 1 (eyewitnesses sometimes/often make mistakes, which is well-known, especially about something as banal about an ordinary car), whereas solution 2 requires us to postulate an entire person (or persons?) who had a motivation to take and then return the car (what? any motivation - e.g. maybe Bill was involved in the drug trade - adds more assumptions).
Let me posit Solution 3: the ranger deliberately recorded his information wrong because he didn't want to be in trouble for not sounding the alarm about a missing hiker.
or Solution 4: the park management/police colluded together to falsify the witness reports to provide doubt to Bill dying hiking to try and reduce the number of deaths attributable to JTNP
Both Solution 3 and Solution 4 seem far less fanciful than Solution 2. Sure, Solution 5 ("Aliens!") would be more fantastical than the u-haul one, but just because the Solution 2 doesn't rely on us changing our understanding of our place in the world doesn't mean it's valuable to think about.
If Bill's body had been discovered buried in the back yard of some drug lord, then sure, Solution 2 all of a sudden looks good. But the situation presented (missing hiker in a place where hikers have been known to get lost and die) does not require that level of attention.
I don't deny Adam contributed more to the case than almost anyone out there, but the u-haul theory doesn't become valuable just because it was he who postulated it.
I think the U-Haul theory was still a valuable contribution, even though it was debunked thoroughly. It honestly tried to make sense of the facts known at the time. Adam's contributions to the case were considerable, even though he always insisted on Tom's contributions being more important.