Orbital layer should be tactical intelligence gathering.

"Actually, the game is a simulation or at least runs at top of a fully simulated environment. The celestial bodies in PA don't just move on tracks, they are fully simulated once they are known to leave a trivial circular orbit for any reason."

The orbital bodies are not fully simulated. The orbital simulation ignores all bodies except for the body that is at the fulcrum of the orbit. This was specifically mentioned in the live stream where they demonstrated the orbital system for the game. If the simulation considers all orbital bodies the orbits cannot remain stable.

"Using the unit cannon to get from a moon to the planet below is perfectly possible, the path is simple and even without active steering, the unit will land right where intended."

If the use of the unit cannon is strictly limited by the orientation of the cannon. You would have a moment where the unit cannon is pointing in exactly the right direction it needs to be to launch an assault for one moment in a 1000. It would be completely useless. They are going to be using approximated physics to make the cannon work. It will launch the vehicles into the orbital layer and they will auto navigate in such a way as to hit the intended target location on the other world. Just like I said. "Units launched from the unit cannon do not have to start out on the correct trajectory. They just enter the orbital layer and automatically plot their course to the other planet like any other orbital unit."

Again, I am not talking about removing the orbital layer. I am talking about removing combat from the orbital layer, and limiting its role to tactical and intelligence gathering. As stated in the title for this thread.

This is not possible. Without the ability to transfer units between worlds, there is no PA.

So your opinion is that without combat in the orbital layer there can be no navigation to other planets in the system?

This is a computer program. It can be set up to work any way the devs want it to. Heck, they could make it so that all units have the ability to teleport to another world. They can do anything they want.

Without a way to navigate between worlds, there is no way to fight between them. Combat is a natural extension of that.