Just going to point out, we are already on their bad side. There's just bigger fish to fry for them as well, but the Restoration is completely aware of just how dangerous Eggman is. They know what we're capable of when we get going.
This statement contradicts itself. An alliance by nature is a major commitment. No one is going to trust Eggman without significant effort on his part. Token effort will get a token ceasefire where everyone is preparing to stab the other guy once it looks like the other guy's guard is down.
Your analysis about bigger fish to fry outside of the Green Hills is flawed. Action economy is the single biggest problem in CK2 quests. It's always about balancing the action economy. We need to crush GUN and the Restoration to get enough actions that we are actually capable of acting on a global stage. How effective do you think we'll be operating across continents if we only have one Heart or Logistics action? Or whichever action they unlock. Any analysis of alliance with the Restoration or GUN must mention the severe opportunity cost of not acquiring the second actions.
It's fairly clear that the Green Hills were designed as a tutorial area for Eggman. He needs to defeat all the factions in it before he can start conquering the rest of the world.
Fair arguments.
Restoration just has not been a direct problem for Eggman in the context of the current conflict, other than Whisper who would've done the same thing if she was completely independent of them. And to clarify what I meant by "token effort" I literally mean the one action to establish neutrality, not continued effort to make and establish said alliance or ceasefire should that fail.
I was focusing on why I wanted to make that minimum effort, which is why I didn't get into it, but I don't deny the opportunity cost of the action economy either. It's actions spent crushing the Resistance and probably GUN for however long that conflict lasts but gaining actions from the rewards vs. actions saved by not getting bogged down in those conflicts and gaining easier access to outside GH faster but not having those extra actions.
There are also the benefits of actions they take against or defending from other enemy factions once we all break out of this bubble, which are problems that Eggman doesn't have to deal with. Or at least not pay as much attention to, since Restoration and GUN will also have to handle it. Two or three factions have more actions than one super faction. To preemptively acknowledge counterarguments, yes, some of their actions will be used in preparation for the inevitable mutual betrayal and thus so will Eggman's. But a significant amount of that is also going to be generalized buildup that incoming conflicts would require anyway.
It's a question of weighing costs vs. benefits, which are going to naturally be subjective based off of priority and how each one is valued.
And keep in mind, I'm fine with the token effort
failing, which is why I don't want it to be more than token. There are benefits to that failure, namely making it easier to keep a hero unit that I and several other people in the quest have shown investment in and the potential of GUN being pulled in multiple directions which would not be good for them.
And to acknowledge what Kingster has said about a genuine long term alliance not happening, I have made all my arguments without the expectation that such a thing was in the cards. Like I said, costs vs. benefits.