Destiny never actually comes into actual orbit with a planet when it picks up a gate in the network. Since these are an earlier version of the gates, they dont have the range of a MW or Peg galaxy gate. But figure the range is within 1k LYs. Destiny seems to follow a path "through" a galaxy. Picks up on gates already installed and in the network. The seeder ships do not follow the path the destiny does. They need to physicaly go to the planed to install the gate. Even a timeframe of 10k years, let alone 1 million gives a seeder ship ample time to do its thing and move on. Plus, a couple hundred seeders cover a lot more ground than 1 destiny. That is also considering any potential disaster, malfunction, or attacks that may delay a ship such as Destiny. It seem apparent that Destiny has been under attack, thus delaying its mission. Even if the ship had issues while it was unmanned it would take the ships systems time to handle the issue.
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