Is "democracy" a preferential system, even when everyone has "just one vote"?

Modern Liberal democracy holds the ideal that we should maximize the liberty of individual citizens while minimizing harms to both individual citizens and the community of citizens as a whole. It's a system that technically tries to be preferential to everyone at the expense of nothing and no one. Needless to say no one actually knows how to do that, but the intuition since the 17th century has been that this can best be accomplished by distributing political power as equally as possible among the entire citizenry. 'One person, one vote' is a slogan that comes from that ideal: it indicates that every person has an equal say in any decision handled by simple voting, and that every person has a voice in the government they are citizens of, no matter how small that individual voice might be.

In practice, every political system is encased within a socioeconomic structure with built-in inequalities, and these non-political inequalities always bleed over into the political system, creating implicit systemic preferences. Politics skews heavily towards the wealthy and the famous — socialites, successful executives, military leaders, the occasional actor — and there is perennial political/legal conflict over whether that implicit entitlement should be ignored or opposed. Further, there is a near constant push-back by people who do not accept the democratic ideal, and wish to establish an explicitly preferential system in favor of those (i.e., themselves) whom they feel are deserving. In the usual case, these preferential groups work against each other, vying in competition, and unintentionally hold something like the democratic ideal through dynamic tension, but occasionally one garners enough power to rise to the top like... err, not like cream, as it were... and become a threat to the system as a whole.

Democracy is messy, convoluted, and contentious, but nowhere near as fragile as it might appear on the surface. Its ideal is very hard to kill, even if its institutions come under threat.

‘Many forms of Government have been tried, and will be tried in this world of sin and woe. No one pretends that democracy is perfect or all-wise. Indeed it has been said that democracy is the worst form of Government except for all those other forms that have been tried from time to time.…’ Winston S Churchill, 11 November 1947 winstonchurchill.org

However, as is patently obvious from the current state of politics and media of all kinds, politics is subject to relatively easy influence by advertising, and less transparent methods, such that potentially any corrupt [dishonest] individual or group could fool the electorate, given that they had the resources. So yes, democracy does give preference to the rich and well connected, and that may be a bad thing.

This seems to be particularly true, given that half the electorate have an IQ < 100, and 100 is not all that much, so they may be easily led. But despite Churchill advocating for democracy, not all systems have been tried. For instance, government could be picked by lottery. This would not eradicate the IQ problem, but it would place some limits on the ability of corrupt individuals to get into power, or to anonymously influence their peers once there.

However, this would not do away with the power corrupts adage, so you still need an even handed system of checks and balances, such as an independent judiciary.

If by 'democracy' you mean 'majority rule', then democracy will ex hypothesi favour the majority and its preferences. There is no inherent reason why those preferences should not allow for and include (at least some of) the interests of the minority, however.

Democracy always has a context. There is never just democracy; it is always constitutional democracy, liberal democracy, socialist democracy, etc. In a constitutional democracy - just as authentic a form of democracy as any other - there will typically be constaints defined by the constitution on the extent to which majority preferences can override the interests of the minority or minorities. In such a context mass manipulation is limited in its force when it hits the buffers of the constitution.

'... democracy is beneficial towards those that can manipulate masses towards some direction, even if that direction would be loosely grounded.' This is true, but it is true of any political system. There are populist dictatorships which rest of the active and enthusiastic support of the majority. There is no reason to think that democracy is peculiarly liable to mass manipulation; and some reason to think that under the conditions of constitutional democracy, especially when buttressed by free speech, free and fair elections, and a plurality of political parties, mass manipulation is checked or restrained more effectively than under non-democratic political systems.