You don't need the whole world to be covered. There is no point dropping special forces into the middle of nowhere. The air force can certainly respond within minutes to threats to major cities and strategic targets.
A starship wouldn't have made that much difference in the invasion of Ukraine. You're talking maybe two additional MBTs.
>There is no point dropping special forces into the middle of nowhere
Most of everywhere is the middle of nowhere and almost everything behind the lines is poorly guarded[0]. The vast vast majority of military strategy relies on two basic facts: things are far apart from each other[1] and one needs to move through another place to get to where one is going[2]. Ballistic transport gets around both of these limitations, which is why it is going to happen, costs be damned. Maybe it'll be drones getting dropped, or bombs, instead of people, but it'll be done nonetheless.
I don't know if you've ever played bughouse - but the timely application of even small amounts of resources can have a drastically outsized effect. A starship could have easily doubled the resources the Russians had to take that airport, a few more could have taken another while everyone was busy with the first.
[0]Because those resources are better spend on/near the line.
[1]Lines vs. back-lines vs. civilian areas, conventional logistics and its demands
A starship wouldn't have made that much difference in the invasion of Ukraine. You're talking maybe two additional MBTs.