Mandate From heaven is most powerful early. If you take it and abuse th hell out of it, you got your picks worth. There is no reason to try and maximize it the whole game. That being said, I see no reason to effectively turn it off.
I haven't had a chance to look at the save game, but I always recommend limited war. If you can put your enemy a whole tier weaker than you, you have accomplished something. Try to analyze teh battlefield and select a single city, that if your opponent lost it and you gained it, you would go up substantially in power and he would drop. Keep in mind he would still be a power, just one you would out tech, out produce, etc. Building nothing but troops to try and conquer a whole civ, can really put you behind overall.
As an example, I took 1 city from the French in my last game initially (early medieval). It was easily assaulted, put the focus on that city going forward (it acted as a citidel defending the other cities, so instead of defending 2 cities I was defending 1, it gave me ivory which I did not have and could not trade for, it also had two other luxuries and 4 iron which I sold off. It still had substantial population left afterwards to be productive (I annexed it). It had the effect of making the french overproduce units as they now had to defend 3 cities instead of one. The tiles had largely been worked, it had granary and aquaduct, two good improvements to have in a conquered city. I also got silver and money as part of a peace deal. By taking this one city I cut out the heart of the french empire and took them from being the continents leading power to being a second tier power. There really wasn't a good reason to take them out of the game yet, and doing so would only open up a huge front with Siam. Later on I launched a massive campiagn and took 3 French cities with my minutemen and cannons, leaving them with 7-8 small cities cut in half effectively taking them out of the game for good. If I researched oil and found out they only had one source, I might take that city later as well and make sure I had the city state oil market cornered.
Good wars can be small wars. Also consider wars of attrition. If I stop my opponents assault and destroy many of his units and gain experience and generate a great general while loosing few of my own, it was a good war.
I would encourage the OP to analyse his opponents forces and the battlefield and come up with a war plan that cuts the heart out of his opponent and reduces him to a second tier power. No reason to try to conquer everything this early.
