Well, that's actually part of the reason why an organization might trade for him. Another organization might see something that the Tigers/Manning haven't been able to adjust that they feel might unlock something and get more value out of Manning.
I always thought Gregory Soto was overrated because of his control issues, his poor BB9. I was quite pleased to see him traded. But somehow or another, his track record of poor BB9 was cut significantly. How did that happen? Its only one season, is it sustainable? Why was this an issue under the Tiger pitching staff (which I think is reasonably considered an asset), but Philly was able to polish Soto up?
I agree with you, though, other organizations see what we can see watching games, looking over baseball reference, baseball savant, fangraphs, etc, etc. So they're going to see those data points, sure. But what do they see that we don't see?