The point would be that a good offense is the best defense.
And both at once is better still. It's a fact that you ARE going to be defending part of the time, and it's another that you don't have to choose between the two as if you could only do one.
You'd also have more of a point if the only concern was defending your cities, but you also have to be able to provide active defense for your improvements.
And THAT would be a point if your UU (whatever it is) were the only unit you have. Come on. You're presenting a false dichotomy here. Just because you have a couple of Bowmen in your city doesn't mean you can't also have some chariot/axes/spears around to stomp raiders. It just means you have something superior guarding the city from attack. What's wrong with that?
Maybe if your opponent doesn't have pikes or elephants.
He usually won't have those in masses, and even if you do run into them lots of flanking will give you a good chance of surviving the encounter, weakening the units for your next camel charge. Besides, what's the difference between that, and saying that Macemen are great attackers, as long as your opponent doesn't have Crossbows or Maces of his own? There's no such thing as a unit with no counters.
However, you're going to find that more often than not a CR3 mace is going to still be better for the bulk of city attacks.
If you measure it simply on victory chance, that's true. But when you figure in the fact that your attack force has lots of mobility, and can take out enemy catapults before they do their suicide runs, and do all sorts of other things that mounted units are good for, it becomes a better choice.
If fighting tanks is ALL you're going to do, sure. Is it?
Redcoat >>>> Panzer. Why? Because a redcoat is pretty likely to actually have to fight another gunpowder unit, while a gunship makes the panzer bonus nearly pointless.
Although I do like the Redcoat better than the Panzer, I don't agree with that last bit. Gunships are highly specialized. They're anti-tank and raider units entirely. You can't even capture a city with them, and they're very vulnerable to SAM and not so good against entrenched Infantry. The advantage of the Panzer is that you can promote it for city attack, and still have it likely survive its run-ins with enemy armor. You don't need gunships to defend against enemy armor if you have Panzers, whereas if you do have gunships you still need tanks.
However, you probably shouldn't overlook the fact that praetorians are as good as macemen versus longbows, but are cheaper than maces. Praetorians are significantly more effective than either swordsmen or axemen at attacking cities regardless of what's defending. What's more is that praetorians also make great defenders, again regardless of what's attacking. Praetorians are easily the best military UU.
Everything up to your last sentence is true. Your last sentence still doesn't follow. The problem with them is their time of utility, which is the Classical Age and very early Medieval Age. For reasons of economy, although I may have a war of opportunity in that period, I don't go all-out then. About the time I do want to go all-out, the Praetorian has become obsolete. So, the Praet can let me do a better job in my brief Classical Age war of opportunity, and extend that a little further because most AI gets Feudalism before it gets Civil Service. Whoop-de-do.
I'm not saying the unit sucks; that would be absurd. I'm just saying it sucks compared to the elevated view some players have of it. It's a great unit for what it does. It just won't be decisive, unless maybe you're playing on a tiny Pangaea and can win by stomping everyone in the Classical Age.
The Praetorian has a lot bigger advantage over the Swordsman than the Samurai, Berserk, Camel Archer, Cataphract, or Redcoat have over their respective normal units, but the others have a longer shelf life and get more use, and that's why I like them better. Especially the Redcoat, which I think is my favorite.
The AI normally doesn't get to mechanized infantry in my games.
They do in mine, but that's because I'm addicted to Huge Hemispheres games. My last war is usually fought with Modern Armor.
Seals are better at defending versus all non-gunpowder units, particularly with the first strikes. They're also good for active improvement defense given they get march, first strikes, and attack bonuses versus some units. I generally have CR3 infantry do most of my city raiding though, while my military city pumps out CG3 Seals and Paratroopers.
Interesting. I seldom have much in the way CR3 infantry left by that time. For attack, I definitely want to use Tanks, with Bombers for artillery. The point about Seals for defense is interesting and I hadn't considered that. The inability to upgrade them, though, still speaks loudly for long-term. But I'll have to think about that some more between now and the next time I play the USA.
A lot less risk if you try to prevent your cities from getting attacked in the first place by taking the initiative against their stack of doom rather than wait for them to pillage all of your improvements.
Well, thank you, Captain Obvious! And here I was just sitting passively on my little backside and letting the enemy come to me.
Of course you take the initiative against their SOD, unless you're a freakin' idiot. But you still need to defend.
Edit: After writing all that, of course I had to play as the Romans, and I got a reminder of the shortcomings of the Praetorian. Playing as Augustus, I had Peter for a neighbor. He was a bit ahead of me in the tech race, but I got Iron Working and Construction; who needs more? Praets and cats, of course I kicked his ass. And then, also of course, my economy went into the toilet even worse than the global economy is doing in the real world.
That's the problem. Militarily, the Praetorian is an awesome unit, but it comes at a time when you can't use it to full advantage. A replacement Maceman or Rifleman with that kind of relative advantage would be overpowering and unbalancing. Because of when it arrives in the game, the Praetorian is not.