Kopitar is better on the boards, but I don't think it's a question who's better at playing in tight small spaces. Size isn't the only thing that matters in that situation. Forsberg was 6'0 205 and he was about as good at making something happen and fending people off in tight spaces as anyone. Crosby is not even 6'0 is he? I'm not saying Lindholm is going to be Crosby or Forsberg obviously but he has that same quality. I'm sure Barkov will be the better player on the boards and using his size and reach defensively, I just don't see him having that same intense create something out of nothing quality in him. It's up to you what you prefer though. I see Barkov in the Kopitar mold, an excellent puck possession player, all around ability, vision, makes the right play 10 times out of 10, won't turn the puck over. I like MacKinnon and Lindholm better because to me they display a bit more of an intense forceful approach to the game (not to be confused with hard work or heart), to me that is a very important part of a forward, although I still think taking everything into account Barkov is the safest pick among forwards in the entire draft, it would be very surprising to me if he doesn't at least prove to be a #2 all around center on a very good team, I COULD see Lindholm crashing far more likely than Barkov, that's why I don't think he has any chance of going as high.
To me Barkov is more like Datsyuk and Lindholm is more like Kopitar when comparing stickhandling. Barkov stickhandles very well in crowded areas, he can steal the puck in a similar way as Datsyuk. Barkov handles the bouncing pucks and bad passes very well. He might not be as good in 1vs1 as Lindholm but i value Barkov's stickhandling more. The thing about Barkov is being effective in the most crucial areas in the NHL. He wins alot of puck battles at the boards, he scores most of his goals from most crucial scoring area in the NHL that is infront of net. He is hard to stop when he uses his big frame and reach at the rebounds. He has ability to pick up top corners and shoot the puck with high velocity and quick release or make quick deke with his hands. That game will work effectively in the NHL. Barkov at times seem to have eyes on his back when he makes plays. He can turn alot of good chances out of nothing but at times he plays just simple game. At times he should use his vision more often and not play too risk free game because Barkov is amazing playmaker and has good vision.
You have very good points on Lindholm but Barkov has alot of abilities too which translates well for the NHL. Barkov plays more like simple and effective. Lindholm is more like patience with the puck.