well, I do not think that navy units should be compared with tanks directly
yes, a tank is a 3-3-2 for 6 and a cruiser is a 3-3-2 for 12, but you can not compare them directly because they will never fight each other
however, you can compare them through the air units, because each will have to fight with air units
tanks are a 3-3-2 for 6 and fighters are a 3-4-4 unit for 10, which is fair or perhaps a little expensive for the tank which should cost 5 or 5.5 or something
fighters are a 3-4-4 unit for 10 and cruisers are a 3-3-2 unit for 12, but the fighter requires you to pay for a carrier, which you don’t attack with, that costs 18, which is an additional 9 per fighter, so that means fighters are a 3-4-4 unit for 19 while cruisers are a 3-3-2 unit for 12, which is not fair for the fighter and sucks my balls (see my post about the cost of carriers)