I agree that the higher levels don't give you as much flexibility in style of play, at least in a certain sense.
That said, I will remark that I've played plenty of game where I've haven't warred in the ancient age or even the early middle ages (except maybe a fake war for a post-Republic GA) on Demi-God, Deity, and Sid levels. Though I've played Deity maps with the AI at most aggressive where I haven't had to war early, I think the easiest way to help prevent early wars comes as to turn down the aggression level (and do things like acceding to demands.. if they come... I've very rarely had them with the least aggressive setting, not settling at a CxC spacing next to an AI city, etc.). So, if you turn up the game level, and don't want to war early, turn down the aggression level.
I also do believe that I've had close (though not necessarily equal to, or very close to) to that sort of production without Hoover Dam in terms of units produced, at least in some sense. As I said before "6. It seems you intend this strategy for a military victory. The point of building Hoover's seems to increase your production of units. In other words, more powerful units faster. With that firmly in mind, it generally comes as better to research to a certain point (Military Tradition, Steam Power, or Replaceable Parts), and then shut off research. Or alternatively, keep researching, but sell techs for gpt as much as you can. You then use the money to buy armies, or disconnect your iron/saltpeter, change builds to horses (try and capture Leo's early, or at least get it as soon as you can), then reconnect your iron/saltpeter on the same turn, but don't change your builds from horses. Then when the horse completes on the inter-turn, zoom to the city and upgrade it to a knight/cavalry. You can get 2 or 3 turn knights/cavalry on plenty of maps with this strategy, especially if you tie this in with short-rushing. In this way, you can get more powerful units faster and earlier than with Hoover's."
Granted cavalry don't have as much force as tanks do, but you don't have as much of a possibility of facing (all that many) bombers this way, and the AIs don't have as much time to train a force for you to kill this way. You also have the possibility of facing more backward units this way. Then again, it does come as at least fair to say that you don't have the blitz ability as you would with tanks, unless you use Cossacks.
Though you can find HoF, and I would guess some XOTM games where tank wars have occurred, I doubt you'll find that the top placing games in these competitions warred with tanks at all, or not that much. I will say that one of my number 1 Demi-God space games had a war with tanks going on shortly before I started building my spaceship in peace at the end, but I did war much more before this with knights, cavalry, cannons, and artillery proper.