It really sounds like you're saying Honka is a sure thing, which is far from the truth. I think it's inaccurate to say that Honka is more likely to become a top-4 D than Pouliot is. Honka is a clearly inferior option to Daley and he's in the same boat as Pouliot. He's not a glaringly better option than anyone.
And the Penguins just won the cup with Daley, Schultz and Lovejoy as their 2nd and 3rd pair RD. They don't need a top end prospect like Honka on their 2nd pair long term to win a cup.
Yes, saying RHD is the Penguins 2nd biggest need isn't inaccurate to say. A potential top pair RD isn't a need though, and especially not at the cost of Murray. That's the biggest issue I have with that proposal. Honka would be useful to the Penguins, but not at the cost of Murray. If the Pens are trading Murray, it has to be for a potential top line LW. RHD is the 2nd biggest need for the Penguins, but that's only because literally every other position is set now and in the long run.
But none of those filled a need. The Penguins absolutely don't need a RWer and a RD isn't a need until none of Daley, Schultz, Pouliot, Begtsson or Prow manage to become a 2nd pair RD. But even then, the Pens only need a #4 for that spot and trading Murray for Honka is blatant overkill for that. The only way trading for Honka makes sense is if it's a swap for Pouliot or if it's buying low, he doesn't fill a big enough need to justify him being a centerpiece of a Murray trade.