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As the title, some competitors I've been watching are using a PBN they (or their agency) have built. I'm looking to get some discussion on how you approach situations like this - do you just report all of the domains to Google and pray they do something? There are 4 sites I'm looking at, all competing in the same niche with very similar websites (different branding and content, but essentially the same pages). I thought all were related, but after Excel-ing all the domains to see which overlap I've found that there's several sets; PBN 1 covers 117 domains that link to competitors A, B & C. Signaling to me that these are owned by the same person. PBN 2 links together B & C with 30 domains, PBN 3 is just C with 40 domains. PBN 4 is just B with 105 domains. PBN 5 is just A with 10 domains. PBN 6 is D by itself with more than 340 domains. Signaling to me that this one probably isn't owned by the same person. It looks like new domains are added to these PBNs every week and this has been going on for quite some time. Now, I'm fully against use of PBNs that don't use authentic websites that provide value, and I can't find any of these sites that aren't just a basic WP template with a single-word text logo followed by spun content. This is a goldmine, because according to Ahrefs these sites are pulling in well over 500,000 monthly visitors between them, and these links make up the majority of each site's link profile. If these networks were to crumble, that would open up a big opportunity for more authentic sites to rank well. How would you recommend to tackle this? Do I find example URLs and write reports for each of the 500+ domains or are there better ways of working through this?

Recently I've had a lot of ideas of sites to build that all would have some sort of relevance to each other, all that would be relevant to my current business. For example, say you have sites for: bars/clubs, music festivals, cinemas, etc, one site for each. While these aren't all directly related to each other, they all kind of fall within a category of entertainment and having fun. Now, I'm not thinking about this as if I were to build a Private Blog Network, but instead each site would actually be valuable to visitors, be content rich, have regular updates and thriving social media etc, as if each were its own individual business. What would be your opinion on actually linking these together at some point down the line? I must stress that these would not be like typical PBN sites where the themes are the same, content is spun or badly written, no human touches or actual value, anything spammy etc, these would actually be authentic quality sites that you would reasonably expect to have a thriving community. Personally, after changing my ways from blackhat to weary-of-linkbuilding whitehat when Penguin 1 was released, I'm aware of what a bad linkbuilding strategy can do and would rather steer clear, however when I compare the plan of these authentic sites I have in my head to the obvious, low quality PBNs that I find competitors use to rank well all the time, I'm coming around to the idea that they may not pose a threat with the way I intend to implement them. Can I get some thoughts?

For some pre-reading, Groupon experimented with deindexing part of their site back in 2014 and found that they had a big drop in direct traffic: http://searchengineland.com/60-direct-traffic-actually-seo-195415 Recently I've conducted a similar test on a very large site and have found that Direct dropped somewhere between 50-80% for the pages deindexed, depending on the day (It has been running for ~4 days). Has anyone else tried this experiment before? If so what were your results?
What I'm most interested in now is to find out why this traffic is classed as Direct - there appears to be no reason why the site or server would interfere, so I can only imagine that Google is sending traffic without referrer data. Does anyone have any thoughts as to why they would do that?