You're keep skipping over the core issue. The 'imminent threat' standard isn't about tying your hands, it's about drawing a line that stops
anything from being labeled a justification for war. 'Justified to whom?' To everyone else on the planet who now has to live with the precedent you set. If 'I believe they'll threaten me someday' is enough, then every country can make that exact same claim about anyone. At that point, there is no standard.
The reason imminence matters is because it forces you to show
evidence of an actual, actionable threat, not just a projection of what
might happen, or as I like to put it..