Soooooo, you're finally seeing it's not probable?
We have no idea what is possible. We don't even understand dark energy or dark matter. We understand that less than the quantum world.
You are like a caveman holding a spear, as I said.
The fact is on the scale of 100s of millions of years or billions of years, you don't need to travel faster than light to colonize an area of a galaxy. The fact that intelligent life evolved here, is evidence it is possible to evolve. Who is to say intelligent life didn't arise long ago and have a 5-6 billion year head start or longer. I'd say it's almost a certainty it has someplace else. Is it rare, for sure, but we have no idea how common it could be.
Who is to say they don't send non-organic machines ... computers to travel to various solar systems ... self replicate and such. When you get to the point that technology and cost is not an option, only time is, on these types of time scales what you think is impossible is actually possible. I don't think humans are destined to be stuck on earth forever. It's not going to last forever. We, ourselves, eventually will have to go elsewhere.