Fair enough. But it's not just the timescales that are relative. One also must account for the psychology of your adversary's decision-making. Risk/Reward, Pros/Cons, the Stakes and how much one stands to lose if they make the wrong call, etc.
IMO, the psychology of a weapon on standby in orbit isn't any less existential threat than the BMs, however to both of your points, it is admittedly more terrifying and destabilizing (initially

). I don't think this is an unbreachable barrier to entry for the concept though.
I'm more or less riffing here, so no shame in dismantling this. I'm not married to the idea.