My point is that "one colonization of a neighbouring planet every 100k years" is a fast speed, not a slow one. A hypothetical alien civilization who got to inte

My point is that "one colonization of a neighbouring planet every 100k years" is a fast speed, not a slow one. A hypothetical alien civilization who got to intelligent life and space-capable technology 1% faster then we did would have a 45 million year head start on us. A hypothetical alien civilization whose development happened exactly like on Earth but on a star which is not as young as ours could easily have a 500 million year head start on us - those are the timeframes on which we have to judge whether they have enough time to reach us; and that is time enough to colonize every planet in the galaxy many times over even at those "slow" speeds. If we ever meet alien life and it turns out that their level of development is just 10000 years behind or ahead of ours, that would be a more unlikely coincidence than having the first stranger you meet have the exact same age and birthday as you do.