There sees to be basic confusion about goals here. Our goal shouldn't be "make sure each party wins sometimes." The goal is "pick the government based on free elections where all people have equal voice" then let elections come out however they come out.

If you just wanted each party to win sometimes, you could just have a constitution with two parties that alternate power every 4 years and no elections at all. But that is oligarchy!

The thing is, we know in a two party system almost always the two parties nationally end up catering to who has voting power and each one wins elections periodically. Democrats have in the past and would in the future cater to those who have disproportionate voting power.

This really has little to do with which party is most powerful and everything to do with which humans have power in the electoral system---who the parties need to respond to.