I'm all for self-promotion, but I really don't understand what the goal is with sub-for-sub? I mean, sub a comic if you like it - I've found a few this way! - but you want engaged readers, right? Trading subs ticks your number up but who cares if the sub doesn't? Unless sub-count increases visibility on Tapas, maybe? (I don't know how Tapas' discoverability works).
I guess there's a networking element to it, but you're not going to garner a readership by trading subs with someone whose looking for the same kinda passion outta you.
I have wondered if everyone on these boards is a comic/novel creator, and if we're all just talking to ourselves, more or less. Do readers come here? I really don't know.