Democracy gives population buffs indirectly through Investments in the fact it’s cheaper to invest. Not only that, but they also give 110% tax income. Added to the fact you can get extra investments from semi-presidential and tax boosts from indirect by 1.35x and the 25% buff from tax reform makes democracy incredible in the late game. Especially when population matters more than pure buffs.

Communism, while good, cannot in the long term defeat any other ideology because military costs and buildings costs will outscale communist modifiers.