The next "story" is not really a story. It seems to be more of a long simile.
The kingdom is like taking a very small seed and planting it in your garden. It germinates, grows to maturity and becomes the biggest plant in the garden. It becomes so big, birds can build their nests in it.
I don't think the point is how it ends up. I think Jesus is emphasizing how it begins. It is small, insignificant and almost unnoticed.
Jesus began with twelve untrained, uneducated people. There were no starts, no special talents and no money. They had more training, more experience when Jesus left, but they were still pretty much regular people. Regular people who turned the world upside down ... with out TV, computers, the internet, seminaries, mega-churches, sound systems, automobiles or smart phones. (The didn't even have land lines. Snail mail really was snail mail.)
Maybe "dominating the garden" is not so much about glamour, gizmos or glitz. Maybe it's about the kind of people we become.