I think he meant "whine".
Your comparison with russia is most accurate, because the AI will behave like the Wehrmacht in WWII. When advancing in late summer/fall of 1941, they had too much focus on controlling the terrain, and subjugating encircled sovjet armies. Therefore they did not reach moscow, which just might have tricked the sovjets to sue for peace.
In the same way you can win against AI. Your border towns against a strong AI might have to fall. But this is not too bad (like it was in civ2). They will be unusable to the AI for many turns. And the AI will leave garrison in them. If you leave just one defender, AI will often stop one turn to reduce cultural defense. The AI will also pillage improvements, which also can split up his forces. All this will enable you to mass a counterattack force. And mass it you must, do not defend like France/Britain in 1940 by spreading out your counterattacking units and try to be strong everywhere. German approach by massing panzers and attacking the "schwerpunkt" works better.
Choose your own fight when fighting a "lost" war. You can afford to lose terrain, improvements, even some cities. But you need troops. When the AI makes a mistake (like splitting up his forces, or leaving his stack in the open next to your stronghold, you take advantage and hit him with all you got. Collateral damage first. After a while your siege weapons stop dying. And then each & every attack you make kills an enemy unit. In the end even an old archer can kill a weakened industrial-age unit. Use all your troops, leave internal cities open if you need. After one such successful assault you will suddenly have more troops at hand than your enemy, and your troops will be more promoted, while all promoted enemies remain dead & gone.
I like to road my entire territory, when I've built most tile improvement with workers. Reason is precisely this scenario - when being invaded. Having roads means you can hit an enemy and run away after. Even if you kill the last enemy in a square. If you don'y have roads around your whole territory you should have road in the 3*3 square outside your cities. Lately I have started chopping the area just around my cities clear so enemies won't get defensive bonuses when I really want to/need to destroy them.
By the way, these wars are a lot of fun to fight. Planning out an elaborate set-piece offense against a hapless target doesn't feel as serious somehow.