How we can tell you assuming you did:
Maybe, just maybe this is the problem as you are just adding more and more work to do.
You can't even get a good article for $10.
Google doesn't want niche relevant backlinks. That's a huge SEO myth.
But what do you expect when paying $1-$10 for a link?
The solution is not more trashy, but niche relevant links
It seems like you are just looking for another reason to convince your mind that cheap links work.
A good domain to setup a pbn on costs anything from $1k to $5k generally. What do you think you get when you're buying even a $15 link? Real hosting is $5-$10/mo. 500 words of decent content is at least $10.
And how do you think they can afford to give a free package?
Because what they sell has no value. It's cheap trash that anyone can setup.
And the 10's of thousands you've dumped into these packages is nothing.
I've dumped 5 figures into 1 single domain for a pbn. Quality is expensive. Very expensive.
300 sites..?
Um. This is your problem.
You can't rank sites that have a handful of articles in 2021.
How many small thin sites do you see ranking?
They are all big.
Build a site with 1000 articles and see how you get on.
I've bought both the expensive and cheap ones, and the middle ones.
They are all basically the same thing.
Even the more expensive ones that won't share the link URLs, turn out to be crap built sites that are dead within a year. 0 traffic, spammy sites and so on. The quality really is so, so low.
You can't really trust random people here either, so when people in the forum "recommend X and Y", it's mostly for some reason other than the link quality. I remember seeing a guy who write quite often on the forum, recommending different sellers in a thread like this one. Later on I read that he doesn't even do SEO, he just spams twitter to make money..
No point giving any negative reviews either. I've done it and all of a sudden I had 200 spam-links from India pointing to my website.