Well for starters i think we always make a lot of assumptions about reywalker. So i agree with you there.
-"Luke wouldnt do that"
-"she was left with unkar!"
People are too quick to say "luke wouldnt!" We havent seen the guy in 30 years. A lot can change in 30 years. Hell he changed a lot in thw 4 years between ANH and ROTJ, let alone 30 mysterious years which we know very little about. Maybe theres a good reason he left her, maybe there isnt. Maybe he made a pragmatic decision for the greater good and didnt let his feelings for rey stop him. Would that seriously make you hate him? I sincerely doubt he did it because he wanted to live a child free life getting drunk at a cantina and screwing anything that moves. He probably had a flawed but compelling reason for it. I think its wrong to assume we still know luke. Maybe he IS in that dark a place. Who knows. All i know is lukes life is shady as fuck and there has to be a reason tied to rey , given the island rey keeps imagining for some reason.
Secondly, we are wrong to assume that he, or who ever left her, left her with unkar plutt. If i recall correctly pablo has said something suggesting not all the visions are events that literally happened as they are shown but may be metaphorical. It could just be that rey was abandoned on jakku and it FELT like she was abandoned with unkar plutt because turning to unkar for help was her only option after that. Hence her vision being that she is being left with unkar.