Calculating the mightiest army in news articles often involves complex algorithms considering various factors like troop numbers, equipment quality, training, and logistical capabilities. It's not simply a matter of adding troop counts. Your 6090 figure from the tutorial map might be a specific value within this calculation for a particular nation, but without knowing the full formula and context, it's difficult to interpret.
Predicting troop strength based solely on percentages is even trickier, as it relies on assumptions about the accuracy of reported data and the chosen weighting of different factors in the overall calculation. While knowing the expected strength could offer an advantage, accurately determining it from limited information remains a significant challenge.