I understand this is a thought experiment, but "if the billions of dollars flowing into Facebook, Twitter, Tindr, YouTube, Netflix, etc. were used to buy or dev

I understand this is a thought experiment, but "if the billions of dollars flowing into Facebook, Twitter, Tindr, YouTube, Netflix, etc. were used to buy or develop medicine" is simply not how money works. The baseline is that -- in the real world -- there are people with skills and equipment and they may or may not put those skills and equipment to use. You can maybe get them to agree to work on producing and developing medicine instead of software. But most of those people and equipment aren't really qualified for that. For the most part, it would just be a huge waste of talent. However, in theory, this could still lead to some kind of progress in medicine (after all, those people are supposed to be smart), but that depends on whether the key to better medicine lies indeed within the field itself. Also, those gains would still have to outweight whatever benefits occur as a side effect of business as usual, for example when an AI that was developed so teens can better sext each other turns out to be useful in automated diagnostics (or something unexpected like that).