Do the invasion beacon troops actually do anything? I just finished a game on Normal/Normal and I saw them leaving my planets, but they had a negligible effect on enemy population and ground power, even with an absurd tech advantage.
If they're supposed to show up as a ground force, they never did for me. The personal orbital bombardment hostile action was the only way I was ever able to take a planet, and even then I usually had to tank their RCI to maximize their death rates.
The highlight was Andors with the Ark. I didn't realize what that meant until I tried attacking them with two planets gone, which meant they were basically unconquerable - +171.5M population per month, and that's after putting their Medical and Public Order below -100 and their compatibility at 0.1.
My racial ground power was over 13 times theirs and I still couldn't get any losses to stick until a small Thoraxian force showed up with about 2b ground power against the Andors' 39b. That was the point where I was actually able to use "tactical support for your ground invasion" and actually do some damage. The Thoraxians got the planet, but it was very easy to bomb them into oblivion afterward.
e: Save is here
, just before sending wave after wave of my ineffectual killbots into their civilians.