Civ 5's combat system is sooooo much better than Civ 4's was.
Very strong argument. Would be even stronger if you could back it up somehow.
Back to the main topic.
Actually, I don't see the problem so much with the surviving of units, but with the fact that
a) units don't retreat in battle
b) conquering territory and holding it doesn't cost you anything in terms of units
a) units don't retreat in battle
If two units with full strenght fight against each other, and one unit (a) will lose 4 hitpoints and the other unit (b) will lose 7 hitpoints, unit (b) will still hold the position, imposing a zone of control, adding flanking bonus to other units, and simply blocking that hex.
This makes for quite some static warfare and can be exploited by the superior human player. Your defense positions literally cannot be crushed, given a halfway meaningful setup.
Since the human understands this intuitively, he is the one who can play around with this feature: the defending unit hasn't lost many hitpoints? Then leave it, where it is and defend even better due to promotions. The defending unit has lost a lot of hitpoint? Retreave it and heal it at no costs.
b) Conquering
When you conquer enemy territory, you don't need to drop units there to supress resistance, keep supply lines open and what not more.
This means, your army used to conquer city (a) some turns later can be used at full strength to conquer city (b). And so on.
The avalanche effect just never stops.
Furthermore, regardless of all promises made before release, it's just the city which counts.
Conquer a city and get all the terrain allocated to it. You don't have to care about territorial control, as this is granted with the city.
Attacking/defending a city almost never requirese more than 6 units. Thus, the bonuses of the AI almost don't mean anything.
So the AI has 20 units to attack you? Nevermind, they will patiently queue up, waiting to be defeated since they can't push you back (see (a))
In total, the whole concept of warfare has not been thought through. Some elements have been thrown into the concept, and nothing fits to the rest.
Honestly, I don't know what they have done during the two years of development. The game gives me the impression that they may have started thinking just during the last weeks, feverishly trying to finalize things, not having the time to correct anything.