I attended TJ from 1998-2002, and my brother attended a few years later, and I've had a lot of conflicting thoughts about this over the last few months as I have watched the decision unfold.
To begin, whether TJ was "America's best high school" depends on what you mean by "best." It was the high school with the highest average SAT score--similar to several Ivy League universities. It had some amazing programs: you could take classes in quantum mechanics as a junior or senior. It had great connections with local private and public research labs for students to do their senior projects. You were surrounded by kids who were smart, dedicated, and competitive.
All that is not necessarily what makes for a great school, at least not in every situation. (For my own kids, I preferred to send them to a small K-12 private school in Annapolis--which has less competition, tiny class sizes, and a lot more art and theater). And obviously some of the things that were good about TJ will be affected by getting rid of the admissions test, such as the SAT scores, while others will remain the same.
I tend to agree with Scott that getting rid of the test entirely was an overreaction, and a hastily-done one at that. What precipitated the change was, around the same time George Floyd was killed, news came out that the incoming class at TJ had no black students. (It turned out not to be quite true, but the number was very small.) People were broadly supportive of reforms. Many supported a holistic admissions process which considered racial diversity. Such a policy had been in place prior to 2003, when the school moved to a race-blind process. Under the prior policy, the percentage of Black and Hispanic students was twice as high, and the percentage of Asians was about 30-40%.
To my knowledge, few actual students, parents, and alumni supported the substantially more radical decision to abandon the admissions test entirely. The Fairfax County Superintendent made the decision with little input from TJ parents and the community as a whole. And, as Scott points out, the primary beneficiary under the specific lottery-based approach the county adopted will be upper middle class white students, who are significantly underrepresented currently.
More troubling I think is the fairly radical ideology underlying the change. Solid majorities of all groups, including Black and Hispanic people, oppose using race as even a "minor factor" in admissions: https://www.pewresearch.org/fact-tank/2019/02/25/most-americ.... Asians are actually the most supportive of considering race, and even then under 40% of people support the practice. At the same time, most people continue to think that high school grades and standardized tests should be the main criteria for admissions: https://fivethirtyeight.com/features/americans-want-grades-n.... Northern Virginia being, in the last decade or so, a fairly liberal place, a holistic admissions process that considered race to built a diverse class--similar to those used universally by colleges--could have gotten buy-in from the community.
More evidence of the radicalness of the approach was the accompanying rhetoric: "meritocracy is a lie" and "admissions tests are racist." Not more nuanced views, such as "some people are excluded from the meritocratic system because of structural disadvantages," or "not everyone can afford test prep." Many people can get on board with such ideas to support things like the prior holistic admissions system. Instead, you had a full-frontal assault on the notion that standardized testing means anything at all, to support abandoning it entirely to move to a pure lottery system. Fully embracing those notions may well result in the "destruction" of TJ as it used to be.
Throwing away the idea of meritocracy entirely is probably not going to have outcomes that we desire, and will be prejudicial to the kids of high-skill immigrants in particular. It is quite remarkable how many doors are opened in this country by being at least middle class and doing well on standardized tests. When I worked at a "white shoe" New York law firm, I had a colleague who had gone to one of "the" New York City private schools. I had never heard of it before. (I'm an immigrant rube, so much so that I had to sell my parents on the idea of my brother going to Yale, which because it isn't an engineering school isn't well known in Bangladesh.) But I could tell it was a big deal by how other people from obviously well-off New York families reacted when he dropped the name. Back in the day, the firm was almost entirely comprised of people like that. Today, the firm is full of people who got there by getting a high LSAT score and getting top grades in law school and cleaning up well enough to look good on the firm website. And while that's not a perfect meritocracy--everyone comes from a solidly middle class family--what would happen if you take away those objective indicators? The ones that compel a hiring partner to pick based on numbers on a transcript rather than recognizing where someone went to high school?