It is the best system that has been allowed to develop given the pre-existing imbalances of power, sure. But liberals have no theory of power, let alone any intention of redistributing it.

What is the point of a free press if the press is owned by billionaires?

How can you have free speech when power controls the platforms from which you can be heard?

What use is the rule of law if it is impossible to adequately prosecute the wealthy and too expensive to adequately represent the poor?

Liberalism is full of sensible ideas which cannot work in this reality. A reality that liberal leaderships are happy to maintain because they hold, and are beholden to, a big chunk of the power that needs to be redistributed. Umberto Eco offers a nice aside on this, in Ur-Fascism:

It was Italian fascism that convinced many European liberal leaders that the new regime was carrying out interesting social reform, and that it was providing a mildly revolutionary alternative to the Communist threat.

Punch left, pander right, act all shocked when fascism takes over.

This is a useful critique of liberalism from a Rawlsian liberal, who admits that even Rawls might not have an adequate answer: The Rawlsian Diagnosis of Donald Trump. Worth reading in full but here's a click-free taster:

There are many other questions we could ask—about the growing influence of money on the political process, say, or about the rising cost of a college education and the obstacle it presents to achieving fair equality of opportunity. But perhaps it is sufficient to take note of the skyrocketing economic inequality that characterized U.S. society during the years in question. Rawls’s claim that his principles embody an ideal of reciprocity rests heavily, though not exclusively, on the fact that his “difference principle,” which governs the distribution of income and wealth, requires economic inequalities to be arranged in such a way as to maximize the position of the worst-off group in society. Robert Nozick once asked, in objecting to the difference principle, how we would feel about a principle that required inequalities to be arranged in such a way as to maximize the position of the best-off group. Nozick’s mischievous question was a fanciful hypothetical that was intended to cast doubt on the strength of Rawls’s argument for the difference principle. But if one looks at patterns of inequality in the United States in recent decades, it is difficult to avoid the conclusion that the basic structure of U.S. society has come closer to satisfying Nozick’s hypothetical principle than it has to satisfying Rawls’s difference principle. That is, the inequalities fostered by U.S. institutions have come closer to maximizing the position of the best-off group than to maximizing the position of the worst-off group.

In short, the United States in recent decades has egregiously failed to live up to any reasonable standard of reciprocity, because its institutions and policies have blatantly failed to affirm the good of all citizens. If, as Rawls maintains, the stability of otherwise just institutions depends on their embodying an idea of reciprocity, then what we should have expected to see as a consequence of those failures is just what we have in fact seen: growing resentment and discord, and the degrading and destabilizing of liberal institutions. In one respect, the situation is even worse than this might suggest. Rawls’s point was about the stability of otherwise just institutions. Or, more accurately, it was about whether a candidate theory of justice could generate its own support if it did not meet the standard of reciprocity. The pre-Trump United States failed to meet that standard, but not because it was attempting to realize a utilitarian theory of justice that relied more heavily on sympathy than on reciprocity, and not because it was attempting to satisfy any serious theory of justice at all. Instead it was simply allowing, or even encouraging, the wealthy and the privileged to prosper at the expense of everyone else. And if even utilitarianism, which seeks to advance the general welfare, contains the seeds of instability because it fails to satisfy the conditions of reciprocity, then what are we to say about institutions that fail to satisfy those conditions because they neglect the worst-off and allow the wealthiest to amass almost unimaginable riches? What we can say is that they provide fertile conditions for the emergence of a candidate, and a president, like Donald Trump.