Hasn't Paradox this sneaky thing going, where they put new mechanics from DLCs into the main game, but only useable by the AI? Thus shifting the balance slowly against the player and forcing them on the long run to buy DLCs to get a fair balanced game again.
Similar to things happening in MMOs with extensions. A new extension usually forces most players to buy it fast, so they can continue to play with the other players, access new raids, skills and gain from the new items on the market.
Not for Stellaris, but considering that their games are pretty much about emergent stories, I wouldn’t even complain about it. For MP only the host needs to have the DLCs.
Similar to things happening in MMOs with extensions. A new extension usually forces most players to buy it fast, so they can continue to play with the other players, access new raids, skills and gain from the new items on the market.