That is fair, but Depay also comes with his own set of question-marks. He is the quivalent of those players you mentioned who have done it in the Championship, as far as the Dutch league is concerned. As I said originally, I wouldn't always go for the younger, lesser-proven talent in these instances - it is a combination of me being a bit unsure of whether Depay is the right player for us, and thinking Roberts is exactly the type of winger I want us to sign, however, he is young and unproven at the top. The question then becomes how far do we think Roberts is away from his potential, and then comparing that against what we have right now. I think we have enough to wait.
You are also right in that I haven't watched Roberts play against good opposition. I don't think that is too important at his age though. He is a young player. He is coming through the reserves. He won't be signed based on how he has played against CL opposition, more a case on how he has played against his own age group, and how much better than them he looks. Roberts has been touted as the best English player of his age for a while now. While that is no guarantee, surely you would want us involved for such a player?
For the record, I wouldn't be that upset if we signed Depay instead, although I think we, and the other top clubs in the land, have an obligation to pursue such talent and get them playing CL football if their talent so permits. I'm not even one of those who is that hung up on us having English players, but where it doesn't come at a compromise in quality, then I'm all for it. It has served us well in the past.