Young Americans is plastic R&B nonsense, but it did lead to Station to Station and the late 70s stuff, which merged the danceable rhythms with art rock. It also helped establish him in the US as a major star, so in that sense it was the proverbial transitional work. At least he worked with people who really knew the sound he was trying to ape.
Agreed. He knew the sound he wanted, and the people who actually knew how to make it. Not my cup of tea, and I would daresay 95% of Bowie fans would agree it's a misstep. But it was the right
kind of misstep, because it took him down another very fertile path. Also, as you said, it broke him in the U.S., which meant he could take the risk of falling on his face in Berlin later. And, of course, it informed Station to Station, where he took what he learned and made it his own style.
Damn, even when Bowie fucked up in the 70s it worked.