The two studies can actually be complementary and not in conflict. The was a problem when the Summers were passed. When they were stopped being passed, the problem went away. The system, any system, has a capacity for smolt production. The summers displaced some winters.

ODFW did a similar, but reverse, study down in southern OR. They passed winters (I think wild) above a natural barrier. Summers were the only salmonid able to naturally pass by. The winters were "successful" in spawning and reduced the summer population. After stopping the passage of winters, the summers rebounded.

In order to be successful, a hatchery steelhead has to adapt to a significantly different environment. They are incubated and reared in warmer water, they are reared in "pools" and "runs" (rearing ponds and raceways) that are not the natural choice of riffles, the are reared at high densities, they are fed food from the surface. All of these actions select for a fish that is genetically and behaviorally different. That is why they need to be segregated from the wild.

The last study, as Salmo noted, shows that you can have both types of fish (hatchery and wild) in a system so long as you keep the spawners separate. Management agencies don't want to invest in the infrastructure necessary to do that. It would also mean that hatchery programs would operate above or below waterfalls/barriers.