"Cheating"/"Savescumming" has an odd place in gaming. It's rarely used in a way that lets the user improve, but it is an extremely powerful tool if you use it in a deliberate effort to improve.
You can create scenarios and practice them, repeatedly, until you have the reaction down. I did that in Rimworld to handle the hardest difficulty raids (now called "merciless", was "extreme" at the time). I'd load just before raid generated, then micromanage it. Just winning wasn't good enough, I did those fights over and over until I could win not only w/o taking damage, but in most cases without even the chance of taking damage.
Similar can be done with Civ. Set a point, then try different decisions and see what kinds of results you get, repeatedly. Find out the most effective choice and why.
I haven't done this in a long time in Civ, because Civ 5/6 on deity just aren't the threats the Civ 4 deity AI was. I only won Civ 4 deity sometimes, despite that I had the most knowledge of that game by far compared to the newer ones.
Note that similar technique to the above is done by speedrunners of various games, using save state practice. "Ironman" modes can be good proving rounds, but if you want to drill to improve at a particular skill you really want to repeatedly practice that skill, take breaks, then come back and do the same thing. That's also how I beat all the B levels in Celeste recently, just have to find all the junk I need to unlock the C stuff.