And compared to other big animals, humanity is less vulnerable.True but that is why bigger animals are more vulnerable. Relatively small disturbances in a trophic web can cause them to go extinct.
Bacteria will likely survive any event on earth except a full destruction of the crust. When viewed as one big group of life, they are very successful in that respect. But that does not mean that no other group can be successful, too.
Humans are the first species on earth with the potential to take life to other planets.
The interesting point in the human population growth is not the growth itself, it is the self-made rapid increase in food production and habitable areas.Bacteria can go from 1 to 7 billion in a matter of days. Point being that "success" has very different meanings and IMO when we talk about the success of intelligent beings we aren't talking abut their numbers or how fast their population doubles.