Yeah, pretty sure he's not going to be an all-star or something...but if he can contribute 20 goals, 40-50 points, that's a fantastic contribution in the NHL these days. Even 15 goals, 35 points in a third line role is a pretty good deal for a guy you pick up for nothing but some cap space.
Also, the whole thing about going UFA basically comes down to some guys are in a position where it makes sense for them to go the full 4 years of college and if they do, they have a chance to decide where they want to play. Some will stay with the team that drafted them and some won't, but most will sign before that anyways because otherwise they're basically leaving money on the table. The incentive to sign a contract with the team that drafted you before you become an UFA is possibly millions of dollars in career earnings. Until it becomes a situation where tons of high quality prospects are passing up millions of dollars to play an extra year or two in college and go UFA, I don't think the "loophole" is much of an issue. It will continue to happen from time to time with some players but ultimately not that often. It's also a reminder (in my mind) to teams that part of their development job is to provide an attractive place to play for their prospects...drafting a player doesn't exactly mean you own their soul, so part of your development process should be cultivating a reputation and culture as a place that players and prospects want to come to.
Finally, I don't think you can just "close the loophole" since it's basically the same rule that allows CHL players or others to become UFA's after 4 years as well and is likely something that is negotiated in the CBA, the league can't just change it without opposition from the players union. The fact that you can't sign a college player until they're ready to leave college isn't a NHL decisions and I think if they could have it the other way they'd do it in a second. That's the real way to "fix" the situation but it's been shown many times before that the NCAA is terrible