Playing on the 3rd line doesn't mean he will end up with 3rd line minutes.
He'll still be on PP1 until he proves that he can't play in the paint anymore. Having your scoring as evenly distributed as possible is more important than loading up top and then crossing your fingers for the rest to fall in place.
He is the guy I'd feel most comfortable playing in that situation. Plus thats a very fast and big line. They lack a playmaker but at least Chytil is awesome at Zone entries and if all else fails, just dump the puck into a corner and let Kreider get it. They'd be a load to handle.
But yeah, I wouldn't have signed him when he was signed and with hindsight, it looks like trading him was a no brainer but this was pre lottery.