Again, not bad advice, but for the wrong reasons.

Wikipedia is a good starting point and a great place to get a reasonably reliable overview. The real resource that Wikipedia provides is the Citations and References sections. These are the sources for the detail in the article and recommended further reading to get to the guts of what you're researching.

Other sources are always recommended. More reliable references are always a good thing and being able to get them cited in a Wikipedia article is a good way of giving extra validation given the process required to get something added to an article. It makes the Wikipedia article better and will cause the source article to appear higher in search results also.

This is a fair thing to ask of people. The explanation is flawed and the advise is a little too firm but in general it is not bad.

If you are referencing a general topic linking to Wikipedia is fine.

If you are referencing a specific thing you should link to the source material rather than a general article. Chances are reasonably good that if your source material is well researched you could get it added to the sources in the Wikipedia article and maybe even update the general article too.

Wikipedia has rules around editing that ensure factually correct information makes it through. Editing can be challenging but if you adhere to these editing can be quite rewarding.