I get this totally and have enjoyed some good fantasy years from A-Rob in the past. I don't think Renfrow is worth a 1st like a previous trade I saw on here but I'd take him over A-Rob easily. Don't like Free Agent WRs that are almost 30 and about to go to a new team. Not to mention, he has never been a great route runner (Renfrow is). I think we just say Renfrow's best season ever but I also think A-Rob's best seasons are well behind him personally. Everything you said is and could be true though.
I don't really care about a FA WR being 30 and going to a new team but Robinson's problems ran a lot deeper then QB play. Not everyone ages the same and he looks like he's lost a step, or two. So I'd take Renfrow over him but at the same time don't value Renfrow like a first, but I'd take a random second over Robinson.