Speaking as an American Succ but who is actually rational and prefers results over ideology (i.e. like much of this sub), I think the biggest takeaway is that a prerequisite for succ policies succeeding are strong institutions to prevent and punish corruption. In the absence of those protections, they may well do more harm than good.

The failures of Succism around the world can largely be attributed the temptation that comes with having control of the government money spigot. Often inefficiencies develop but they aren't dealt with because the powers that be need to maintain the recipients in order to maintain power. Those range from inefficient programs key voting blocks want to rewarding control of state owned companies to incompetent but well placed figures in the military.

That and protectionism. Protectionist tendencies, which fosters its own forms of corruption and corporate welfare as the beneficiaries seek to profit and prevent being beaten by better foreign competition, has been a huge anchor on left wing developing countries.

More mixed economies (and open for global trade!) are generally able to do better against corruption because the free market making those propped up inefficiencies less tenable.

Young democracies may well not have sufficiently strong institutions that they can support a robust social state without it rotting or backsliding into authoritarianism but with a red coat of paint.