Air national guard is part of the AF. The first EX were literally given to Oregon national guard lmao. ANG does not exist as its own service, and many would argue is an unnecessary service in and of itself, which is why it's trying to argue for its existence.
Upgrading existing airframes is cheaper than buying entirely new ones, obviously. But the sales of newer 4,5 for the US are political. Russia can't make 5th gen in proper usable numbers, so flankers are a necessity. J-20 aren't one-to-one with flankers in capabiltiy and weren't designed to be, they actually need their missile trucks and EW platforms, plus they aren't procured in enough numbers. J-35 once it reaches its numbers is where the parity would lie. Israel, I'll give you that one, but if they had the option for F-22 I doubt they'd choose f-15. France will never buy F-35 due to protection of domestic industry. The Euro consortium also in turn needs to maintain their own industry with purchases and upgrades, plus bought typhoons can't be left to rot, and the Typhoon is a better A2A platform.
Point is, many of these stem from either domestic industry issues or the F35's design being a strike platform which does not suit their needs. End of the day, if you want a multriole strike fighter, brand new panthers are better than vipers and seemingly not more expensive.