RE 1. I can't imagine any YMYL search for which Wikipedia isn't an order of magnitude better result than content marketing garbage that currently occupies the top spots. Sure, the official website of the relevant government or organization would be best, but Wikipedia is almost always second best, and currently neither of those are the most likely results to get.
I know in theory Wikipedia isn't trustworthy, but in practice, it is good enough, and its form does a lot of work here. Most entries are structured to be information-dense and fluff-free (unlike the content marketing crap), and they cite their sources (unlike both content marketing crap and many official government sources). This overall makes it one of the most useful resources for generic health queries.
RE 2. I wouldn't complain if I was doing "buy" queries. I don't do those often anyway (for similar reasons I don't use shops for product discovery[0]).
--
[0] - https://news.ycombinator.com/item?id=19643059
