I don't think it is trust as much as it is desperation and seeing no other options. They tried it alone and got no where at all.
Ryder as a hero or not so much? Hmm. You know something? I don't know. I am not blaming the writing for this or anything but I never felt attached to my Ryder enough to think about it and I'm uncertain as to why.
I am oddly indifferent to him. Maybe too often he doesn't say what I'd actually want him to say? I don't know.
I guess he's as heroic as he needs to be and I know that sounds like I'm copping out on the answer but I'm just going to say he's very heroic very fast because he needs to be as his mission is essentially to save every race that came from the Milky Way so the usual slower progression into hero isn't possible here.
Okay, you guys just witnessed me thinking out loud. I hope we all feel closer now. Lol!