This is maybe starting to veer a bit off-topic, but...
(Btw, I agree with you.) I'd like to discuss this: I don't think that growth itself is the problem here, it's the nature of the growth. Consider the CLV, the customer lifetime value. (I admit that I hate my economics classes with a burning passion but hey, they're unfortunately extremely useful.) Simplified, the CLV is how much profit (income - cost) a customer brings the company during their whole "life" as a customer of the company. In general, it's much more profitable to have a few long-time customers than many short-time/one-time customer, due to the cost of acquisition (in this case, probably ad costs). The latter category often even incur more cost than profit! And the risk I see right now is that tapastic is mostly attracting that very category.
Simply choosing viral and popular stuff a majority of the time leads to a homogenous kind of userbase: They'll come for what's popular at the moment, but if they're not given anything unique to stay for, they'll only stay for as long as the "hype" lasts. If they simply come for "BL" or "gags"... They can find that elsewhere. Gag-a-days are ubiquitous, they're all over instagram and co. The CLV of these readers will be very low, if not negative.
But if tapastic promotes seriously good comics of all genres, as in quality over genre, the new readers will find very compelling reasons to stick around! The series itself doesn't need to be exclusive to the site - but the selection of quality needs to be unique for tapastic. They'll notice that they can find better and more varied stuff here than on the rest of the internet!
This goes for all genres. Any comic that runs long and can keep readers engaged over a length of time is economically worth promoting for tapastic, and I'd wager that far from all readers only read one type of comic. But even if I say "all genres", what kind of comic probably engages the most emotionally? What tends to run for the longest time? And what tends to be neglected on the front page?
Long-form story comics.
Balance it out. Have a section on the front page with promoted quality entries from a wide spectrum. You'll be able to hook a wider variety of readers for longer periods of time, even if your growth curve might be slower at first.
So there y'all have my kind of economically founded case for promoting select quality comics of all genres instead of blanket genres with high viral ratios.
Okay yes it's off topic. Sorry.