The planet defenses.

[Tsagoth]

But there are a number of colony defense options that don't require the colony to be productive: mine deployment ships, cruiser and battlecruiser transforms, or just leaving a fleet in orbit.

I'm curious about that feedback, then. People thought those options weren't good enough, or people didn't want to actually spend resources defending their new colonies?

Mine deployers, and the ship conversions didn't exist then. All of those things were added later to try and address the problem of protecting newly placed colonies.

You would drop a colony and somebody would come by with a pair of cruisers and that was it, colony gone.