There is no real merit-based admissions in the US. It's mostly very subjective. That's my feeling as a foreigner who trained in a Chinese-type meritocracy, where there were anonymized written entrance exams for every educational spot, every few years, thus making sure that they were taken by the brightest, not the most connected or charming. Not only that, but higher ed was free, so I have more than 8 years of it. The medical system was significantly public and governmental, and all the public jobs were taken based on similar written exams, no favors. I never really appreciated that system until I came here, where a person with barely passing USMLE scores can take a coveted anesthesia spot if s/he's well-connected or -liked. Let's not speak about AA and "diversity"-based admission/hiring, which are anything but merit-based. Oh, and specialty board certification is a joke, when compared to other developed countries, even in anesthesiology (which is one of the toughest), and now it's close to worthless (except for employer liability purposes).
Also, some well-endowed private universities love to admit people based on future predicted income, because they need rich alumni for donations. That's why parents matter to them; if you are from the right background, you will make much more money after graduation than the poor schmuck who worked his way up from the slums. Of course, they will also take some of the latter, because the smoke looks good in the mirrors, and they get to be "diverse", and qualify for federal loans etc. The criteria for college and later admissions sound absolutely ridiculous to a foreigner; e.g. what does volunteer crap or sentimental Hollywood-ian essays have to do with somebody's intellectual potential? In a meritocracy, all they would care about is knowledge, not race, not face, not wealth, not connections etc. Interestingly, we never had rape problems in higher education, possibly because truly smart people have more respect for women.
One more thing that is far from a meritocracy is immigration, btw. Canada and many other countries have point systems that give significant weight to education, occupation and experience, especially in jobs needed by the national economy, even age (and remaining productive years). There is limited family or religious immigration, and forget any chance of permanently immigrating without passing a serious language proficiency test. In some countries, you even need an attestation of "assimilation", where you have to demonstrate that you have local-born friends and truly belong to a local community of non-immigrants (church, club etc.).
tl;dr A non-merit-based system breeds injustice (and corruption), and injustice breeds resentment, frustration and extremism. Everything that public money touches should be 100% merit-based with no chances of human manipulation, even if it takes taking 3 times as many (and tougher) exams in a lifetime. Like that will ever happen...