" If time travel is possible ", therefore... what?

Following Nick Bostrom's "simulation argument" formulation ( https://en.wikipedia.org/wiki/Simulation_hypothesis ), the "time traveling argument" could be expressed like that:

If in the universe time traveling is possible, then modifying the past is also possible, then creating new branches of time is also possible, then at least 1 of the following propositions have to be true:

1) the fraction of living species in the universe that reach the point where they can achieve time traveling is close to zero,
2) the fraction of the living species in the universe that are interested in time traveling is close to zero,
3) the fraction of the branches of time that have been created by time travel is close to one.

So if 3) is true,
* therefore we are very likely living in a branch of time that was created by time travel,
* therefore it's very likely that our past has been already modified by time travel

https://www.quora.com/If-time-travel-is-possible-does-it-mean-it-has-already-been-used