As far as I know, there's an idiom 'David vs Goliath', so what is the opposite called? Say, how do I describe a war between two equally strong players?
You can say that the warring factions are 'evenly matched'
Evenly - adverb
3- With equal amounts for each person or in each place evenly distributed/divided
Incidence of the disease is fairly evenly spread across Europe.
The two teams are very evenly matched (= are equally likely to win).