Seems pretty obvious to me.
If I spend $500 on an item, I am still spending $500 on the item regardless of any mail in or checkout rebates. If they give me $125 mail in rebate for purchasing the item, I still had to spend $500 buying the item to qualify for the $125 rebate. Once I send it in, sure, the $500 I spent on the item can be said to only cost $375 because I made $125 from the rebate, but I still had to purchase the item for $500 and then mail in the rebate.
If I spend 500 FPs in a swap with a friend, I am still giving them 500 FPs to their GB so they will give me 500 FPs in mine. Once their GB levels, I will get 125 FPs back, but I still had to spend 500 FPs in the process. Like a mail in rebate.
Sure, I can then spend the 125 FPs on whatever I want, but I still had to spend that 500 FPs to get them. It can't be factored in to reduce the cost because it didn't. I still had to spend 500. Sure, I get 125 back, but I still had to spend 500 to get those 125 back. If I didn't spend the 500, I wouldn't receive the 125 ever.
Of course, I could CHOOSE to put those 125 FPs right back into my GB, thus reducing the leveling cost, but it doesn't directly reduce the leveling cost, and I think that's the main argument here.
Sure, I could choose to do that, but I could also choose not to. So those FPs don't directly reduce the cost, but indirectly reduce the cost if I want them too.
I think that's what's being discussed currently. The rest is just opinion.
Ex: would I invest those FPs right back into my GB, thus reducing the overall cost to level? No. I would save them for whatever later. Thus they don't reduce my GB leveling cost.
Would someone else just toss them right into the GB they're leveling? Absolutely. And it would then reduce the cost to level said GB.
To each their own. Fancy economic language doesn't really change this point. Still gotta spend the FPs to earn any back, and then have to choose to put them right into the GB you are leveling in order for them to be considered reducing the cost.