It depends on the situation. Realistically, a lot of political systems will struggle or fail due to human nature. Theoretically, these very same political systems are likely the optimal political systems if you could assume perfect conditions. Ultimately, it comes down to how much human is involved in the political system, because humans are ultimately the irrational decision maker that ruins otherwise functional political systems.
For example, in practice a dictatorship or other monarch-based systems are usually flawed due to a large amount of political power being concentrated in one human. This means that this power is easy to be misused, due to a lack of checks because of a single authority with power, and it makes power fluctuate on the condition of the person in power. However, in a theoretical perfect situation of an infallible, fair, and immortal monarch (essentially a god), a monarch-based political system would work fairly well, as power is concentrated in a stable and just source. The weaknesses in a practical monarchy become the strengths with the right person at the helm, due to the nature of the political system. However, due to human nature, this perfect being for a monarchy will likely never exist, making monarch-centric political systems inherently a flawed structure.
Meanwhile, in practice, a democracy is usually a more stable form of government, due to the people in political power being held in check by the people they represent, and other balances within the system. However, democracy has it's own flaws in practice due to, again, human nature throwing a wrench into the system. Politicians are supposed to make decisions that benefit their populace, but these decisions are difficult to make, and often have multiple answers with no clear way to predict success for a lot of them. Furthermore, not all politicians will act in the best faith of the populace, and the populace may not be informed enough, or motivated enough, to protest about it. The balance against power abuse can fail to check the abuse due to the public obliging the abuse of the person in power. In addition, democracies are often ineffective when the population is too large, yet it is most effective when the population in the democracy is almost equal, if not equal, to the population that will be influenced by the decisions of the democracy. That being said, democracy is generally more stable as a political system due to tools in place to moderate the political system from overreach.
But, in a theoretically perfect environment, democracy becomes inefficient. If every individual is a perfectly informed citizen, and each politician is motivated and population-driven, then democracy slows down effective governance because the very same tools intended to balance powers will also slow governance. Election cycles require the efforts of politicians to be divided away from their core job of governance. Furthermore, actions within a democracy are subject to scrutiny from the population of which it serves, which further bogs down governance, as informed decisions are not reached overnight. Also, democracy is built around compromise. Unless every politicians can agree on the right course of action to take 100% of the time, then the very nature of democracy will slow governance because compromise will be necessary for progress to be made among dissenting parties. And if all politicians did agree on the same course of action 100% of the time, you might as well do away with democracy and replace it with a monarchy, as it would functionally be accomplishing the same thing.
Basically, I think every political system works in an isolated bubble that sustains the right conditions for it's success, it's just those conditions may not be replicated in reality. There's characteristics with any form of governance that can be both a strength or a weakness, depending on how that characteristic is used. Concentrated power is fine if the person in power is omnipotent and benevolent, democracy is fine if the population it represents is informed and active, and the politicians involved, but fallible. Capitalism is fine as an economic system if checks and balances prevent economic Darwinism. Socialism is fine if the limits of government influence is checked at population necessities. Communism is fine if the resources available meet the needs of the population and the distribution is impartial.
What ultimately matters from the political system is, in my opinion, that it meets the needs of the worst off in society. We don't measure a society's worth by how well off the people at the top are, but by how well the people at the bottom are. Who cares if the emperor of the nation lives in decadence if his people subsist off dust and decay? A political system never succeeds, in my eyes, unless it can meet the necessities of everyone it is supposed to represent and protect. If a person at the bottom of society can go through life without basic existential worries, then we've given that person the bare minimum of decency.