I agree with the Redondo/Rijkaard analysis - that is, I agree that the role he plays here isn't the most obvious fit for him. He looks like a more natural fit in a co-called pivot role of some description - behind an attacking midfielder/playmaker, slightly behind two central midfielders, in a diamond of sorts, yes. Although Real's version - with Redondo in it - was slightly different from the Milan diamond. I'd say Redondo would normally find himself higher up the pitch than Pirlo did.
However, I can easily see Redondo in a midfield two of the old sort - and in a modern-day two-man pivot like the one employed by Real in later years. I hate the term "pivot" by the way, but I use it myself all the time, fecking hipster jargon.
Anyway, the point would be that while Pirlo, say, would look entirely out of place in that role (one of two central midfielders in a diamond) I don't think the same can be said for Redondo. But I fully agree that Rijkaard looks like a more natural fit. If you don't have Rijkaard - you could do worse than use Redondo (who is, after all, just about the complete midfielder). But if you DO have him - well, why not play him? I really don't see what Redondo does in that role which would justify picking him over Rijkaard.