As a perpetual ranter about the silliness of the admissions process and in particular how tone-deaf most administrators are w/ regards to the struggles of low SES students, I feel the frustration. I've had the opportunity to have many talks with admins from a top 10ish medical school and while I'm sorry about your experience a lot of medical schools are really doing their best considering the situation. I'm addressing each one of your main points below.
1. Volunteering is much more easily undertaken by students that don’t have to pay bills. Clinical experiences (paid and unpaid should be treated equally)
This is true, but from my experience talking to admins they are treated equally, with many schools (at least the ones I know of) preferring paid vs unpaid. I personally don't believe that the type of activities considered clinical experiences (doing anything as long as it's close enough to smell patients) are relevant for the admissions process. Volunteering in a hospital does not shown selflessness, just the fact that you have free time. Actually working with patients, whether that's by taking up a CNA, scribe or EMT position is much more relevant exposure to the medical field and again most adcoms see right through the BS.
2. AMCAS needs to make practice tests and resources more easily available. Test prep companies price gouge students because they know that 50% are from the top quintile and are willing to pay whatever it takes. This prices out low income students.
The FAP gives you access to a wide range of prep resources and the AMCAS-Khan Academy partnership is a step in the right direction. Sure, not everyone qualifies for FAP, but you really don't need a prep course that costs 1000s of dollars to do well on the MCAT. You could argue for expanding FAP, but knowing the amount of effort it takes to write quality test questions (plus testing them, ensuring test security etc.) the fee is decently fair and the cutoff for FAP is quite generous. But screw test prep companies. They're scumbags.
3. I do not honestly believe that schools like Columbia are seriously considering all 1000 students that they invite to interview. Honestly kinder to have a smaller pool.
I think it was
LizzyM that talked about the ladder concept, but yeah. Columbia probably did not seriously consider all 1000 students. The tiered post-II communication is indicative of that, but I personally know someone who despite being relatively mediocre in their application, nailed the interview and got in. N=1, though. Having a smaller pool would be predominantly detrimental to low SES students that don't have the resources to build a stellar application.
4. A significant number of students (at all schools) are admitted due to legacy status. Legacy is cancer for both undergrad and med school
Wouldn't really call it significant, unless you describe legacy status very broadly, but otherwise agree with you. Back-door dealing is despicable, but an argument can be made for a school accepting students from their own alma mater or relatives of their alumni as they are much more likely to enroll.
Again, I'm really sorry about your experience in the process and I don't think anything I'm saying will bring any comfort. I'm sure you'll end up being super successful wherever you end up going; but the current admissions system is miles ahead compared to almost everything in the world as far as ensuring fairness. Could we do better? Sure. And we're moving more towards that. But universities have a high degree of institutional inertia and any changes take ages to propagate even if everyone is incredibly well meaning.