it's not too low because the googlebot freaks out when it sees a new domain acquiring 100s of backlinks in a short amount of time. In its fake intelligence the googlebot will deem this sudden influx of backlinks as gaming the system (which it doesn't like), and will sandbox the domain name. It's happened to one of my websites last year, I've built the website in February, did no backlinking for 2 months, then I got pissed off because I saw no rankings (not in even in top 100 of the results page, much less page 1.. or even page 2 rankings), and like I said, I got pissed of waiting for google to reward the "great quality content" (which I obviously had), and I started building backlinks by purchasing a diverse backlinking package (which included all of those things you mentioned and more). About 1 month after having those backlinks delivered the website started appearing in top 100 for 2 keywords, one at #86 and the other at #88. It's stayed there for a week and then vanished again from the SERPs. and then I got angry again and totally ignored the website until september if I remember correctly. In september I purchased another one of those "great" SEO packages hoping to get my rankings back but it didn't happen. And in January this year I got about 4-5 guest post / PBN type of backlinks from various websites related to my niche and the rankings have come back within 2 weeks of those backlinks being indexed by google.
Google has devalued those backlinks a lot, it's not necessarily hurting your website if you get them, but it's wasted money because they carry very little linkjuice value. Guest posts and PBNs (and occasionally web 2.0s) are the backlinks that rank you. Well, this is only regarding backlinks, but google takes many factors into account when deciding where websites rank, and some of those factors are extremely important, such as user experience (how clean and fast your website is for visitors, and how quickly they find the answer they are looking for), domain name popularity (how much traffic the domain name gets before being ranked in google), and many others.
So anyway, if he wants to test things out on his own - which I highly recommend since a huge part of being successful at SEO is testing things out because google updates their algo dozens of times a year - then he should do so, and he'll see what works and what doesn't because each niche ranks differently for each keyword. But if he doesn't have the time or money to test the backlinks for himself he should just stick with guest posts acquired at a safe pace (a few per month for 2-3 months, and then increase the number by a few more backlinks gradually) in the beginning and his website will be fine. Yes, this takes time and his keywords might rank even sooner than 3-4 months, especially if they are low competition keywords, but he'll play safely at least
