I share the frustration, but I don't think Bednar is an idiot. He seems like a pretty intelligent and thoughtful guy. Also the only coach to have won championships in the ECHL, AHL, and NHL as head coach. That's meaningful.
If there's one thing in common with all coaches, it's that fans hate their line combos, and don't understand why they use them. I remember Wings fans would constantly give Scotty Bowman shit for his lines, but he just kept winning.
There's a reason why he's being so stubborn with his lines, especially when he's also known for using the blender. Whether that's a good reason or not I don't know, but he has to know Nelson is struggling, and Marty worked well with Nelson, and is the kind of player that helps him.
I think part of it is he wants a heavy forechecking 2nd line with Val and Nelson. This exact line with Val and Drouin on Nelson's wings played outstanding their first game together. Problem is a lot of that was because Val was in beast mode, and he seems to have lost his inner beast. Make of that what you will.
I also think Nate has a big say in this. He likes having another highly skilled winger to work plays with.
Hopefully Bednar realizes the lines haven't totally been clicking the first two games and switches them up for Game 3.