"Fair shot" is overrated in the bottom six, you can see in a few shifts whether a player has the fire to succeed in that role, and in a higher role, whether he flashes enough skill.
That doesn't mean a player who shows those flashes is a lock, rather, if he's not showing those flashes on a regular basis, he's not NHL ready, if he gets a few shots to do so and doesn't show them, he'll probably never be NHL ready.
I mean how many shifts did you have to watch Farabee to know he was a NHL talent?
Vorobyev has had three shots at making the team, while poor linemates may reduce your "counting" stats, your relative metrics should be solid despite them if you're playing well. The eyeballs can see skating speed, quickness and agility, passing, forechecking, backchecking. Vorobyev simply doesn't stand out on NHL ice.
Where an extended trial is needed is to figure out just how good a player is and whether they are climbing the learning curve or have reached their career plateau.