Laine is the playmaker on that line. He is not a one-trick-pony pure sniper, like everybody think he is. Great overall offensive player, carries puck, makes plays, snipes. If you put any other playmaker there, it leaves another line without a playmaker. = less depth.
Obviously the chemistry with Ilomäki isn't working in a best possible way, but there's not much other options without making other lines worse.
Yeah the great thing about Laine is that offensively he has a complete talent. He has it all: shot, vision, hands, size, skating. He wont ever be the most explosive player on skates but he is learning how to use the skate. I know they have been working with his skating position, which was a major problem for him, and its looking better and better.
His defense is far from complete but he still has some defensive qualities that will be elite level in nhl. He backchecks aggressively and has size and strength to help him. When on offence his off the puck movement is good. Knows where to wait for one-timer and wants the puck all the time and is in right places to get it. Defensive off the puck movement is pretty bad and is constantly in wrong places. He can save some of these errors with his physicality and athletism. Lacks a lot defensive awareness.
Even thought he is complete offensive player i would still think he would be best utilized in sniper-role at nhl level. Best thing about him is that he can shoot from a pass and he can create a lot changes from himself. When you have Laine on ice you want constantly feed the puck to him because that's where he excels. Thought you want to give him the puck in the most advanced position where he can create scoring changes for him and linesmates. Thats why he aint a typical playmaker style player. Also he isnt "200 ft" player and most of his strong defensive abilities shine in offensive zone and middle zone. But with his endless offensive talent I strongly believe that with right kinda center he can be a 50+50 superstar. He also has gamebreaking abilities and hunts for goals. He is the one who can give you overtime goals in Stanley Cup finals.
The main reason why i believe that he will be a superstar at nhl level is that in the end what seperates superstars from the rest is their mentalside of game. Laine is really looking growing into a superstar role and all his daily activity goes into being the best hockey player on the planet.
edit: Laine is lucky be in Tappara because they are magics in making big players skate better. They are working with ex-speedskater Risto Rosendal who is superb skating coach. The main principle in his teaching is to get better skating position. Butt down, head up. That way your balance will better and you can see ice all the time. Tapparas/his trackrecord is better awesome in teaching big players to skate. Barkov, Lehterä, Kontiola, Laine etc. They all were horrible skaters when they came into his training.
