Thank you,
@Victoria for your explanations/analysis: I knew the air-naval-ground-AA system was broken, but never realized how badly and in precisely what numbers (like I said, I don't play much Late Game: I think I've built all of 2 air units in 2000 hours of playing!)
Looking at the Naval Promotions reveals another set of anomalies, unless they've changed in GS. The Naval Melee has a "Reinforced Hull" Promotion giving a +10 defending against Ranged Attacks. By my reading of the Posts above, that should include defense against Fighter aircraft attacks, but still gives the Destroyer a measly 80 versus the basic Fighter's 100 - enough to avoid being One-Shotted, but not what you'd call impressive. Naval Ranged has the "Proximity Fuse" Promotion giving +7 against all air attacks, which is, frankly, even more mediocre than reinforcing the Hull. Naval Raiders (Submarines) are as they say in Boston, Scrod, because they have no Promotions giving any additional air defense.
@Sostratus and others. . .
I think part of the problem is that Civ 'lumps' everything that has happened in military technology for the past 70+ years into a single 'level': after WWII Battleships, Destroyers, Aircraft Carriers, Fighters and Bombers you get a few Promotions and one incomplete set/level of new units: Jet Fighters, Jet Bombers, Missile Cruisers. This is a gross simplification of what has been happening. Just to take Naval Missiles, there have been two generations of Cruise Missiles, three generations of Antiaircraft missiles, a whole new category of Point Defense systems, and the massive armor plate of WWII-Era Battleships and Heavy Cruisers has been replaced by electronic jamming, 'spoofing' and 'stealth' techniques. In a nutshell, in 1945 Defense consisted of being able to survive most hits. Since then, Defense consists of not being spotted or hit at all.
The result is that 'modern combat' (Atomic-Information Era) in Civ is a hodgepodge of mis-matched Units: Jet Fighters that represent capabilities ranging from the F-86 of 1951 to the A-10 of 1990 to the F-35 of 2018 (or their MiG, Su and Euro equivalents) ALL IN ONE UNIT. Frankly, that's like representing Alexander's Hetairoi, medieval Knights and WWII Tanks all in one Unit: it doesn't work, and 'works' (is allowed) in the game only because, apparently, neither the designers nor the players realize what a Crock it is.
Now, I don't think an entire new set of late-game Units is the answer. For one thing, there isn't time to develop and build and use most of them by then, so the return on graphic/design investment is, frankly, marginal.
That's why my argument is for a set of Technical Upgrades similar to the GDR's.
So, at, say. Tech: Rocketry you could Upgrade Fighters (and later, Jet Fighters) with Air to Ground Rockets increasing their factors against ground and naval units. AND you could Upgrade Destroyers, Aircraft Carriers, and Battleships with Antiaircraft Missile Installations giving them an increase in factors against ALL air units.
At Tech: Guidance Systems you could Upgrade those Antiaircraft Missile Installations to Homing Ground-to-Air Missile Installations with even more AA defense against All aircraft, while Jet Fighters could be Upgraded with Fire and Forget Air-to-Air Missiles for more effect against other aircraft, and so on.
This would allow far more differentiation than the linear Promotion System and speed up the differentiation/specialization more than a new set of Units with resource and Production requirements.
Just my thoughts.
