I tried stuffing my size 3 colony with cores and it did not to add anything Pathers on Hostile Activity. That seems like legacy from previous releases. If so, then the way to colonize the sector would be like before, never let alpha-run colonies grow past size 3 (which is what I would have tried in the last release if I had bothered). On those small colonies sitting on huge +2/+3 deposits, use an item that boosts resources another +3 to have production close to a size 6 colony.
My plan for colonies this release:
* Pristine Nanoforge in Orbital Works (+quality, meet supply demand for Military Base/HC)
* Synchrotron (meet fuel demand for Military Base/HC)
* (Maybe) one or two other items.
Have no intention of using cores unless I wipe Hegemony off the map first, and only if Pathers do not interfere, which they seem not to if size stays at 3.
I probably would like to use the Hypershunt Tap, but it also requires other items that produce +3 commodities in other industries and maybe AI core to reduce demand in P&I.
I probably would like Hostile Activity more if it means no more pather cells at +7 interest on one planet provided Hostile Activity level is kept low. I would have liked to use the Mining>Refinery>Orbital with forge chain, but the Pather cell that resulted made that option a no-go. (I avoid whack-a-mole Pathers at all costs.)
P.S.
The idea of mass colonization of size 3 worlds was to get P&I income from dozens or a few hundred colonies after I blow up all the core worlds (which destroys all income from trade) because either my commander is a maniac who wants to conquer/destroy the sector, or he is sick of all the expedition spam (on his colonies or the incompetent two-faced core worlds) and wants to make it stop by killing everyone.
Ah! Honestly, I think part of this is what scale one expects player colonies to have. I don't see the game as a 4x and ultimately colonies will let you do a few specific things and you won't need many of them for that, and these point values are tuned with that in mind. More on the "a colony with an alpha admin and some cores is special" side of things, rather than "so I have these 4 credit printing machines stuffed to the gills with cores", if that makes sense.
Might want Pathers to count size 3 colonies to close that loophole. On the other hand, counting size 3 worlds would make Tech Mining bad since Tech Mining itself adds up to +8 interest (on the biggest ruins).