Europe prospered under democratic governments after the second world war. My particular region of Germany was rural, agrarian and piss poor before the war. Now it is an industry hub and one of the richest regions in Germany, all thanks to a democratic government, which prioritised development of rural areas.
The wealth we now enjoy is incomparable to what we had under authoritarian rule before.
Let's also not forget, that the Cold war divided Europe in two halves, one with democratic governments and one under authoritarian rule, an A/B test so to say. The end result was, that they needed a wall in Berlin to keep the people from fleeing to the west.
> Look around the world and see how many countries managed to achieve similar success using the same liberal principles
Beside the whole of Europe, Japan, Canada, Australia, New Zealand, South Korea, Uruguay and Taiwan come to mind. Taiwan has a per capita GDP 2.5x that of mainland China.