Why have more ranged units in an army?

I genuinely don't understand this. Granted, I have only played Cathay to its fullest and me and my buddy were getting our butts kicked when I had a 60:40 ranged to melee ratio

Sure you can bog down a couple of enemy units with your melee frontline, but the rest of the enemy tries to flank and go for your ranged units, and since you have more ranged than infantry, the ranged units would be defenseless

We only started winning when I put 8 to 10 units of spearmen to completely protect my 5 ranged units.

Enlighten me please how more ranged units are supposed to be the meta? Advice and brutal criticism are welcome lol