Ah, good, some of you are seeing why I claimed MI was about as powerful as MA....
But in case you missed it, let's do a thought experiment. Team 1 will have 11 MA and team 2 will have 12 MI. This is an equal cost.
We'll have the MI dig in and sit in a size 10 city, a reasonably common occurance. Along come the tanks. They have an attack of 24 vs the defense of 30.3 (18 +50% for city +25% for fortified *10% for open terrain). The tanks will lose 55% of the time, plus there are not as many. So a few are going to be held in reserve.
The MI attacking the MA is going to be 12 vs 21.6 (16 +25% for fortied +10% for open terrain), or a loss of about 65%. Worse odds, yes, but there are going to be about half as many MA as MI, bringing the odds slightly in the MI's favor. Many of the MA won't have the chance to fortify, and will be weakened from attacking.
This is a reasonable situation to see, and it illustrates the need for COMBINED ARMS. If either side had some artillery, or if both sides had both types of units, they would be better balanced.
But where my eariler claim really falls on its face was that MI costs MORE THAN a regular Tank, but it is DEFINITELY more powerful. Tank: 16-8-2. MI: 12-18-2. The MI has 50% more attacking power vs the Tank's defending power, wheras the Tank's attacking power is only slightly above the MI's defending power. MI can also master Infantry, especially if they attack the MI. You still don't want to attack MI with MI though.
The other problem was that when I thought of costs, I was remembering my mods, where I bumped up some of the costs. Tanks are a few million dollars. A whole army of spearmen couldn't stop a company of them from doing whatever it wanted, but would cost less.
Which brings me to another point. Anyone notice how MA (and tanks and MI to a lesser extent) are so fast that your support units can't keep up? You can either over-extend yourself smashing enemy cities with tank-rushes and risk the survivors coming out and wiping out your undefended assault arm, or you can delay your attack a few turns to let the artillery and infantry get into position, and risk having a ton of extra defenders and a bogged down attack. I made this effect even worse when I bumped up the speeds of all mechanized units by 1, but it really gives the Blitzkrieg feel to the game; the German Armor constantly had to be slowed down so the Infantry could catch up and allow for proper combined arms operations.