The issue when I worked at the tower wasn't how quick we could launch them, but how quick the surrounding airspace (mainly centre) could accept them. Given the lack of radar coverage outside of about 90nm (ovbiously depending on height) meant we had to have at one point, 2 mins between departures on the same SID. That went away but we can still launch them quicker than Centre can accept them. Would more radar help? I don't know, I am but a simple tower controller
