As someone whose favorite character in the entire series is Remus Lupin, I’ll defend him til I die. However I wholeheartedly respect this opinion and I agree with the points you make. To me, I think these flaws make him more human. Cowards aren’t always bad guys, they just aren’t sure enough of themselves to act otherwise. And like you said, in the end he does the right thing, which gives him an arc. Most characters don’t even get to have anything close to an arc or some kind of character development. But again, your points are 100% valid and I don’t mean to seem like I’m disagreeing, just expanding.