You're on the right track here, but I think subs actually do even less than that. While I'm unsure if empty subs are actually harmful (which is so commonly said on Tapas but never confirmed it's almost like an urban legend), unless you are new and get a massive spike in them, which might put you in "Trending", all subs actually achieve, mechanically, is unlocking certain features (ie, the ability to get ad revenue and then the ability to get ink, which of course can be manually unlocked anyway at Inksgiving).
Based on my observations, I'm pretty confident to say what actually moves you up the "popular" ranking in the current algorithm are likes! When I get a spike in likes, my comic moves up accordingly. I think it's based on likes during the last... maybe 24 hours?
So getting subs can be useful, but usually only IF those subs are engaged readers who will reliably like your latest update. If you have twenty people who like every update on the day you update, you will gain reasonable visibility to people who scroll through specific categories. Their views will also generate ad revenue, because why even unlock ad revenue if you're not getting views to generate it so will never actually claim that money? If you have twenty people who have clicked "subscribe" but don't read, don't comment, don't click "like"... well, you have a number that is 20 higher, but no actual mechanical benefit in growth from it.
The only other factor I guess is that comics that appear to be more popular might attract more readers through herd mentality, like a lot of people will go "Oh, wow lots of people are reading this, I guess it must be good!" BUT sub counts are actually kinda hidden now. What's the number written under your comic in the popular rankings? It's likes! You don't actually see the sub count til you click on the comic. So again, likes likes likes! They're the currency you want to chase.
