Dubas did the same thing in Toronto when he let Hyman walk & traded Kadri. He's not a good GM.
His problems in Toronto: goaltending & D. His problems in Pittsburgh: goaltending & D.
Toronto fixed both as soon as he left. He doesn't know how to build a team.
This isn't true IMO.
Did Dubas have blunders? Absolutely, but every GM does.
Kadri being the biggest blunder for sure, but guys like Hyman would have re-signed had the cap not been flat.
He also didn't leave the team with any anchor contracts and left them with some great pieces(Knies, Woll, McCabe, Tavares).
Even in Toronto, he improved the D a ton, (Muzzin, Brodie, McCabe, Giordano, Schenn) all great adds at the time.
You are right about goaltending.
All in all, he couldn't get it done, and a new GM is here to try changing that, but he could have left the team in a much worse spot.