If takeoff is fast, then it's unlikely that two independent superintelligences develop

If Takeoff takes a short time (days, hours), then it's very unlikely that we'll have multiple projects leading to superintelligence.

One of the projects will probably have completed it's takeoff before other projects can start.

Similar logic can be used to say that if takeoff is slow (years, decades), then there's a high probability there will be multiple projects going to takeoff.