Why would a species want to colonize a galaxy? You’re talking about insane travel and communication times after all, and spreading very thin. Sticking to a single system or handful of systems while controlling reproduction rates is a solution that achieves the same ends without spreading your species so far that it amounts to a million different civilizations. At some point over such distances you’re not colonizing anything, just throwing generations into the night with no hope of a return. That same energy could be used to engineer a structure or structured for those same beings to live within a reasonable distance of each other.

The whole Fermi Paradox reasoning is flawed, because the assumptions are flawed.