One thing a lot of people seem to be missing with this is that it lets you remove a ridiculous amount of threat in a single thwart, which can then be doubled by Overwatch.
Normally, thwarting Overwatch with a basic thwart is going to remove 2-3 threat without self-voltroning. Some identity cards will remove 3-4 threat. Each your allies would remove 2-3 individually. But together, they can remove tons of threat at once.
Assume for a moment that the characters are averaging at 2 THW per character. With 3 allies, this removes 8 threat which triggers Overwatch to remove 8 more. That's 16.
With Utopia, you can get an extra ally in on it. Now that's 10 from Peacekeepers and 10 from Overwatch, for a total of 20.
If your allies all have Danger Room Training buffing them, you can potentially thwart for 26 at once divided between two schemes.
That's not relevant in a solo game. It's even overkill in two-handed. But it's going to be incredibly useful at higher player counts when you're the Justice player tasked with taking care of threat.
I believe this particular combo is the real value of this card. Not the ability to distribute the threat removal as you please, though that's obviously useful as well, but the ability to produce insane threat removal in multiplayer and double that threat removal with Overwatch. Especially since you can use this to help complete powerful player side schemes that will benefit the entire table.
That said, at lower player counts where you have to fill more roles than just being the person to thwart schemes, Gunboat Diplomacy is probably better.