I don't disagree with your assesment of the player, he doesn't have an amazing shot and he's a great passer/playmaker since he has very good vision.
That being said the style of game he plays will always lead to goals IMO since he plays around the net all game long. A lot of tips, rebound goals, pucks going off of him and etc. A lot like Holmstrom, he always had a similar amount of goals and assists. Tkachuk is better than Holmstrom all around, so as you say I do expect more assists but it'll depend on who he's playing with. He's a type of player that could play a Stone-like game playing with a guy like White like we saw at the end of the year. He was more active when away from the net, leading the rush in the Ozone, turning pucks over. If he plays with guys like Brown and Batherson though his role will be significantly different. He won't be the guy controling the play so he'll likely be more in front of the net.
I think he's a very adaptable player with his skillset.