Why would you stay put and take Harrison, when you could accept this offer, move from 27 to 23, and still get Harrison?!
The only way good the Cardinals to extract more from the Vikings in this scenario is to threaten, or actually go through with, a trade with the Giants. But then they risk having the Giants pick Minnesota's preferred QB, which prevents the Vikings from making a deal with the Chargers, allowing the Chargers stay put and take Harrison.
Frankly the Cardinals should either play some higher stakes poker where they still HOPE to get their preferred WR but risk missing out, while receiving a "haul" of draft capital in return.
Or they should accept ANYTHING in a deal where they're guaranteed to get Harrison at #5, because they have no leverage if they want that guarantee.
But sticking at 4 and taking Harrison in the face of an offer where they still get Harrison plus ANY additional draft capital would just be foolish. It doesn't matter if they lose points on the draft value chart, because once you net out Harrison, they gain value.