Everything is based on the quality & number of tier 2 links while choosing the domain you want to get links from,
This does include PBN domains, Guest posts websites, etc... And the core thing to check for these are the RDs & the quality of links pointing into them,
So, basically, you should really care for tier 2 links as they do half of the job,
The case can be different for the PBNs & Guest posts as you only should aim for genuine natural tier 2 links from good websites but the concept is basically the same, it's simply not worth building quality links as a tier 2, but lower decent quality ones that do get indexed and pass some links juice do work pretty fine
So, the only problem you'd have here is no focusing/building or not on tier 2 links but the quality of these built and the right ones that should do the job,
For that, you should rather go for less number and aim for some higher quality, typically some good web 2.0s built open expired articles (could be spun 5-10 times) with long-form content, pics, a couple of headings... Which should be picked up by Google and do have some value at least
