It's fine. In my experience promo forums don't really work as people would like. Since a lot of the time it creates phantom fandom.
On the other hand, I will promote my story once I publish it, but I won't spam each forum since I see no point in it.
And I honestly don't have the time to do a sub 4 sub scenario. It helps a lot but if I sub to something I want to be able to read it and truly help the author.
If I can't read it (due to my limited time) I don't think I am really helping them.
I do know that helping them reach 100 subs is a lot of help but I want to truly help them and not just phantom help them.
Having said that, there is nothing wrong with being a phantom sub/follower. I just feel the point of being an author is making the day of at least one person and personally I value more a dedicated fan over a sub. But that's just me. Some authors value more subs.
Getting back on topic, I have noticed that forums that have like 1k posts don't really help with your promo. Mainly because new members that join the forum don't have the time or patience to read all 1000 messages and to sub to each and every comic/novel.
Something I don't like from the promos I see here is that most members just promo to promo without having a target audience. For example, if you promote your last chapter without explaining what your story is about, then you won't truly create an interest.
Marketing should always be done with a target audience in mind, not just spamming without a target.