Speaking as a Wikipedia "volunteer" (or rather "editor"), I think it is in fact a very good idea that the Foundation takes no editorial responsibilities (except reacting to legal challenges via so-called "office actions"). It means that editors don't have to worry about legal, sysadmin, PR, etc.; and conversely WMF is not directly responsible for Wikipedia content. Believe me, it would be silly for WMF to be involved in all editorial disputes about what should or shouldn't be on Wikipedia, how things should be formatted, etc., in all languages.
Basically, the foundation is managing the playground where the editors can build an encyclopedia (along with other projects, e.g., Wikidata, Wikimedia Commons, etc.), and then mostly leaves the community alone (with some exceptions, not all of which were well-perceived). Given the scale of Wikimedia projects, I don't think 300 employees is excessive (it's very little when looking at other sites in the Alexa rankings except Reddit), and it's great that the expenses can be supported by donations so WMF doesn't have to depend on other people than readers.
I don't see why I would mind that WMF staff gets a salary and editors don't -- editing Wikipedia is not my full-time job, but running it is theirs. (In fact, to the extent that editing Wikipedia is part of my job as a public researcher, I already get a salary from my institution...) It's easier to manage Wikipedia content with volunteers (where most processes don't depend on one single person and where there are little firm deadlines) but to have paid staff to manage operations (if the website goes down you want someone to have a look immediately). OK, it would be conceivable that the foundation could offer grants to pay some full-time editors, or redistribute money as small gifts, or as a lottery, or something, but it raises a lot of complicated questions (I don't know whether the topic has been discussed before) and I'm not sure it would be worth the effort.
Another important point is that the WMF is not a company but a nonprofit, so it is reasonably transparent, and many people in the staff are chosen through elections. It's not like individuals are getting large dividends from donations to the WMF.
I my opinion, the most important point to keep in mind is that WMF asks for volunteer work, but the outcome of that work is shared on fair terms with the public. If I want, I can just grab their entire database https://dumps.wikimedia.org/ and software https://www.mediawiki.org/ and start hosting a mirror with the data, and I have both the technical possibility and the legal right to do it. So WMF is not like companies who ask for volunteer work and then keep it behind closed doors (e.g., the volunteer Google Maps editors, or the historical CDDB example https://en.wikipedia.org/wiki/CDDB#History).