"I do not think the claim that they were "very Christian" is plausible."

I do claim the mainstream of people fighting for Hitler were very christian (of those who had any religion). Not that the hardcore inner Nazi circle was christian (probably none of them were).

"The Catholic church condemned the Nazi ideology as contrary to Christianity (in Mit brennender Sorge)"

But they only did so, after Hitler attacked their organisation, not before or after the Nazis rose to power. Hitler did not liked them, but had respect for the catholic church, as a old power institution. But he did not had them under control as the pope was elsewhere, so they started to attack their base. So not so much a question of morality or religion, but mere power in my view. But surely there were also quite a few Kräuterbein's (if you happen to know that book). Who did not went into open resistance, but did what they could to keep things sane and humane.

"and large numbers of protestants took the risk of condemning the "German Christian movement as heretical (e.g. those who joined the Confessing Church)"

I have a huge respect for those who did. But I don't believe their number was that large all in all. The majority marched in line.