Alright,
My view point is understanding why sub4sub culture exists here in the first place...
Problem here lies in Tapas having two sets of growth model...


There's Comics and Novels section affiliated to Tapas Media which has some sort contracts with these artists and writers.
And there's Community tab section where Indie Creators content are seen, where creators are hoping there work would get noticed and algorithm pushes it.
But in order for Indie Creators to get their work recognized, the Tapas ain't pushing the newly posted Content by new signee who just onboarded platform, but rather some old Indie Creators Content with millions of views under its title... and it is showing like as "recommendation" or "You may also like this"..
I am like I just got here why you showing me some BL comics or some stuff I like... I haven't seen anything or liked anything yet.. (when I had clearly selected slice of life category as my preferred choice on platform)
At first I thought...well ok may be this how this webcomic platform operates for comics and novels stuff...
Then there was flood of Tapas affiliated content in my inbox..
By this time it was all too apparent...
Tapas was pushing its own content and other Indie creators content as recommendations which it thinks has best probability of gaining more engagement and raking in more ad revenues for itself and hopefully some for the Indie creators...
I was like fine... what other options does this platform has and oh boy this where the Tapas Forums comes into picture..
Signing into forums... I came across all these pro artists in either off topic or questions or Art/comics section... and I am like wow these art works are amazing why isn't it showing up in community tab section or recommendation...and also I came across new artists or writers and other amateur artist myself included
with little to no views... and there in promotions thread was my first experience of sub4sub culture at that time didn't give much thought to it did it anyways..
Full disclosure I created a topic on sub4sub myself long ago... the curiosity piqued in me to see what unlocking that 100 sub milestone would do... and result is it has no effect...
I feel the only thing sub4sub & like/like did was mess up the algorithm, a algorithm designed by Tapas Media which was recommending content what it thinks is the best bet for itself (the affiliate tab section and Indie Creators content which had gained significant traction) and pushing it on as recommendations for new creators who onboarded it.
Imagine if such sort of tailored specific algorithm was created by YouTube oh boy... and while on same context look at YouTube, they even removed the trending button and now content is more of a user personalized experience and it recommends new content related users search history...
Do you see where I am getting at... You either revamp the algorithm where it creates a even level playing field for everybody.. And not where Tapas see it as two different categories of growth model such as affiliate and Indie creators but rather whole thing simply as content...
I think if you guys did this there wouldn't be even the need for the existence of this Forum as well... new contents are recommended based user experience hence there wouldn't be even any need of promoting outside the scope of Tapas App itself... You could save your resources and deploy your developers to focus on other backend operations. (I also understand comics has become highly fragmented and oversaturated market but this where user search history comes into play doesn't it...)
Also I feel your ranking systems are once again has flawed logic, its like once again you want cherry pick something or other content and decide for others what content they might like... why perpetuate same problem of platform again and again... you either rely on your algorithm to do the work for you or you don't.
As far as your original question I think its a futile exercise... reason being if you ban sub4sub in promotions thread as many have already mentioned above its going trickle into other categories or private messages...and lets say you ban it its gonna create a avalanche of promotion threads.. right now as it is Forums promotions thread is basically a spam... (no one pays any notice to it)
My honest request is you revamp your algorithm on main Tapas site where it creates level playing for everybody... I feel at its core this will take care of new creator visibility and engagement issues... (also with no views and engagement I think it can act as feedback to creator themselves who can change the direction of their content and see what works and what doesn't)
This just my assessment as a Reader and as creator on this platform for the past 2 years... I may be wrong on this algorithm thing.. I wonder how other Indie creators feel about this algorithm.