I think that's a bit of a generalisation. That approach can work the other way, for example - a few years back, Carlton had four rucks in Kreuzer, Jacobs, Warnock and Hampson on their list. No way they'd be keeping four, so the Crows took a chance on Jacobs after 17 games and gave up picks in the mid-30s and mid-60s.Ideally we need to be cleverer than that.
You need defensive forwards - one way to go about it is to look at a team that has millions of that type and take the least effective one that they might release. So you end up with the least impressive guy from a team that has four or five of those types.
There is a better way (and no way are MFC looking capable of this). Take Geelong. They identify a need for defensive pressure and flexibility in the forward line. They trade in Rohan - everyone laughs because we've decided he is a useless spud. And it turns out that they correctly identified his skill set as something they could slot into their team and turn into an asset.
Unfortunately we are probably dumb ****s who won't learn how to do this.
So, there's examples of this approach working both ways if a club is smart enough with its list management approach.
In regards to the Richmond small forwards, I think they've all shown they're AFL-level, and it's an area where we're severely lacking. So it makes sense to try and prize one out - and we wouldn't be paying too much unless it was for Rioli, who I assume they'd be least likely to let go.