Kulak is definitely a bottom pairing guy, for some of the reasons you stated, like a lack of passing ability and making some iffy decisions in his own end that separates those types from the front line guys. But for a bottom pairing I think he's close to as good as it gets. Good skater, physical and seems to play within himself. Of course with Nurse out, his minutes and important time have been elevated, and then some holes get revealed. I hope they can sign him.
As for Kulikov, he seems to be playing very well, although sheltered on a deep team. I thought he was terrible with us and did not shed a tear when he left.
The one of the main difference between the two is last year Kulikov was asked to play Keith's current top 4 role, plus shutdown minutes with Larrson; while Kulak is getting sheltered minutes on an offensive pairing with Barrie. Funny enough, that's same role Kulikov had a lot of success in before arriving here, as he primarily played with Subban in NJ.
I don't think Kuluk would have as much success if he was asked to play with Ceci on a pure shutdown pairing, with Nurse back to babysitting Barrie.
Off topic rant, but one thought that went through my head a lot last year is Holland should have gotten both Murray and Kulikov out of NJ.
Nurse-Barrie/Bear
Murray-Larsson
Kulikov-Barrie/Bear/Bouchard
That would have had Kulikov in a more comfortable role, and Larsson with a defenceman that could play shutdown minutes (Remember, Murray-Savard was CLB's 2nd pairing for years)