Unfortunately, that generalization doesn't work because the policy slot is ongoing rather than one-time.
So
One-time effects+ policy slots
V
Non-policy slot ongoing effects
By Holo! Have you still not understood that you're just playing word-games with yourself that literally have nothing to do with the actual idea of "ongoing" or "one-time" effects? A policy slot is a one-time effect (getting an extra policy slot) that has then a permanent effect for the rest of the game (having one more slot than you would otherwise have), and depending on how you look at it, both are right. It's "Getting an extra Policy Slot." vs "Having an extra Policy Slot.", purely a matter of perspective when it comes to the semantics. But this whole discussion is meaningless, because this was never meant to be a discussion about semantics.
What people are referring to when they say one-time effect vs. permanent effect - or at least what I was referring to in that other thread, of which this here seems to be a continuation of - is how it works mechanically.
When you build the wonder that grants +1 Policy Slot you are granted a perk that says "This player has +1 Policy Slots!", then the wonder does literally nothing anymore. That's the important one-time effect. You get something. That something is then completely independent from the wonder. That's why when the wonder changes ownership you keep the policy card, because you lost the wonder, but you kept the perk (Civ 5 didn't use a perk-system, but it used the same idea of wonder-bonuses being mostly one-time effects that fire once, change something in the database and then are completely "decoupled" from the wonder itself).
Of course, this would be easy to change. Just make it so the perk transfers with the wonder when it changes ownership. Would probably be a bit of work to catch all the ways that wonders can change ownership, but it's possible in theory.
The argument against doing that is still consistency. Things like being granted a free Tech, being granted free Policies, free Great People, free Promotions, free Population, free Eurekas are all "one-time effects" mechanically, and not all of them can transfer in a reasonable manner. Technologies being an obvious one. How do you actually take a technology from another player? Do you set them back to the tech progress they had before? How do you deal with missing prereqs resulting from that? And did they really somehow lose the knowledge they had because a wonder was destroyed? No, that's just dumb.
So what it really comes down to whether you prefer having some extra wonders that can be conquered for their effects, or whether you want a uniform system that makes sense when you understand it.
Both sides have some reasonable arguments when it comes to that, but I find myself on the side that prefers a system that is consistent within its own rules.
