Terry's upside is that he gives you the occasional difficult to pull off offensive play like that goal against Colorado. That sort of difference-making can't be taught so you wanna give it every chance to succeed.
His problem is that he's a black hole of consistent suck outside of those plays. He makes the wrong pass constantly, misfires the right pass when he finds it, gets bumped off the puck and off his feet way too easily for a guy his size, and has shockingly stone hands. If he already has the puck solidly under control, he can dangle pretty well. But he really struggles to settle down pucks as they come to him.
When you watch him play, count how many times per game the puck goes to him or his vicinity and then the next player to possess it is an opponent. It happens constantly, often multiple times per shift. Hockey is a possession game until you get to the scoring areas, and Terry is where possession goes to die. He's often the opposing PK's best player.
Fans see the two goals in Colorado get jazzed. I'm a fan, I was jazzed, they were jazzy goals. But scouts also see the first shift after his second goal, where the Ducks tried to break out through him on the half boards three times in 45 seconds and he turned the puck over under minimal pressure all three times. The two goals is unusual for him, the puck yakking is not.
The potential is there, sure. You can't teach his size and you can't teach his offensive skill. If he could become functional at all the little stuff, he has top 6 potential.
But I don't see how that makes him much different than, say, Sprong.