@Vantelli, I think many things have changed. Building from scratch and get your site on good position, seems to me harder than it used to be. On the other hand posting good articles on already well positioned websites is working pretty well on my side. I guess the website itself has gained reputation or trust from search engines, I don't know.
Ironically, long, well structured articles are not being fully read by visitors, but still they are well positioned. I posted about this on another thread as how readers have become dumb, there I explained how the contact from visitors started changed (by email) from average to actually pretty dumb questions. Anyway the traffic is there and the new articles get good positions. I don't exactly know what to say about long vs short, but I'm convinced quality still matters.
Back-links? I used to exchange links, post on discussions (I had content that qualifies as answers, reports, research, etc, not just articles), I was also an active member on some specific forums about certain stuff, example: spaceships, I wrote about it, did research so I was an active user that could post useful stuff and experiments about space ships. It wasn't low quality, it was good quality on my niche, great effort. Besides this people, students, whatever... posted articles pointing to mine, that also built back links. My point here is it's been YEARS since I don't do that anymore, I never spent time again building links (I know I should).
For whatever is worth, and I hope it helps you, I based my work on what's been posted here on WebmasterWorld as good advice: good original content, research, post with structure, titles, semantics, pictures (I took time to work on photography, I'm also a photographer) and when you mention how expensive freelancers are charging you today, I can't help but remember how it feels creating good articles, I did it, and did the same work for others too (as a freelance webmaster) the funny thing is I'm not looking forward on doing this again. I got the feeling it doesn't matter how much I charge, it's not a fair pay, only if I do it for myself. (I feel it that difficult).
I don't mean to criticize what you posted, but MFA (made for adsense) sites kinda match your description. No bad intention here, I mean focus on one topic, from there as you write about it (like space ships) you will surprise yourself on how many more articles you need to expand or just to explain that same article (rockets, energy, the sun, gravity, etc. Each important word used on your main article actually needs it's own article. I used spaceships because we can't use specifics, spaceships serves better than widgets in this example.
It takes time... and effort. I don't exactly like my own advice here but focus on ONE website and put your efforts there, then expand. Paying someone it's valid, explore the possibilities on doing it yourself, it will give you a better sense of direction, where to go.
*Posted about 100 articles* you said. In my case, from advice found here many years ago (wouldn't question anyone who does it differently) but it works in my case: create your 100 articles but don't post them at once. Create your structure and set an order, post 3, 5, then 2 per week, when you see bots visiting you constantly to crawl then go 1 every two days or daily, but only good content. And as much as I dislike this, post on facebook groups, FB is not magic, but a lot of captive traffic moves around there regarding your topic.
*** In case I confused you up there, I mean creating good articles it's not easy, I stopped doing it as a service for clients despite whatever they want to pay me, it's an effort I'm only willing to do for my websites. I see it that hard.