First of all, I don't do GSA links for every property I own. It was just an idea to get back in some niches, while waiting for my main sites (two of them) to grow slowly via pure white-hat. Betting is a hard niche, but it slowly grows.
In the meantime, I've tested some other sites with GSA and got mixed results. But I've skipped the T1 properties (except for some PBN domains) and went directly with links to my main site, with articles (90% dofollow).
It worked amazingly for a while (and for some kws it still works), but it slowly died. There may be some reasons for that. I got lazy, stopped writing more articles and used spinning too much. Or maybe I got into a penalty of some sort.
I got hooked on GSA and Scrapebox, while working whitehat on my other sites. In fact, Ahrefs showed me a lot of BIG sites are doing blackhat, even without a buffer of T1 links - they just link directly to their moneysite. Maybe they get away with it, since the valuable, authority links are already helping their site, and probably GSA links don't matter.
I am looking at one site now and see it began growing two months after it started to post links "GSA style". I've been able to do this only once
However, the big boost in traffic occurred after 10 months.
Now, long story short, I have a question: how long does it take you to rank in top 10 or top 5 for at least some of the kws you target, on a niche that's "hot", meaning PPC is higher than $1.
In fact, I have one more question: do you use a lot of web2.0 properties (blogspot, wordpress etc)?
Edit - A third question: since some of the GSA links are perfectly valuable links that can't be associated with seo spam, maybe the key lies in the speed of submitting? How many links per day/per domain is too much?