Hi Peter,
Ok, first let's address the quip, "You get what you pay for." This is always a knee-jerk reaction by people who typically refuse to do any "due diligence" into whatever the topic is. I have worked for over 20 years on Open Source Software projects. The root of many of these projects is "crowd sourcing" the underlying source code and build tools of the software. We would not have the internet and all of the software that is being used to run the internet, without Open Source Software. It is a common fallacy to say, "you get what you pay for", because that assumes that there is nothing of value that is free (without some monetary cost). The people who say these sorts of things are being closed-minded. Now... having said that, there absolutely has to be due diligence into whatever it is one is looking at. The better phrase to use is the Latin phrase, "caveat emptor", or "buyer beware".
Second: Yes, there are a lot of different DNA tools and "materials" out there. It can be a bit confusing. I can't say that I have a full grasp of everything yet. There's just not a single place to go for everything. I think it's because genetic testing, and using it for genealogy, is still so very new. But it keeps getting better and as it does, it keeps getting easier for people. But I think it still has a long ways to go in terms of ease-of-use.
I agree with Robin, in that there seems to be a lot of people who do DNA tests for just their "Ancestry" or countries-of-origin, which is really not about genealogy. There is so much more they can do with their DNA tests, but they are either uninterested (don't care), unable (don't know how), or unwilling (want to stay private) to do any more with their tests or genealogy.
Lastly, to your question, "What is WikiTree not doing with DNA that could be done better?" That's a really good open-ended question. I'm sure that there are many others here who have a better view of the state of the art who can better answer that question.