This idea has been brought up before on here -- I can see where the suspicion arises, especially when you look at the forums!
But as others have said, it doesn't hold up when you take any large comic and look at the profiles of their subs, and count how many of them have their own comic -- the vast majority don't. I used to give out thank-you notices on my subs' profiles, and a loooooot of my readers were people who looked like they'd just signed on through facebook to read comics and never bothered to do anything with their profile.
This is also pretty normal on the wider internet! Creators in years past scratched their heads over the popularity of comics like Ctrl+Alt+Delete and Dominic Deegan, while something beautifully drawn and poignant like The Locked Maze was never really noticed on that large a scale. It's why we say there's a healthy does of luck in this game -- getting an audience isn't something that automatically comes with quality.
While I have seen a competition mindset emerge on sites with subscribers, I don't think it's common. One of the big reasons I've always liked the webcomics community is that it ISN'T viewed as a competition -- I don't have to worry that if you read Joanne's webcomic you won't read mine; you can read both. And skilled creators tend to be the ones most vocally supporting other comics that they personally like.
You'd have to be really petty to go around liking episodes you don't really love and avoiding interacting in any way with the episodes of comics you genuinely enjoy. But more importantly..... why would those people interact most with comics that are already popular? If you're threatened by competition and feel like you can't get ahead because of other comics stealing your audience, why would you then strengthen the hold of the really popular people who are "stealing" your spot on the front page? Wouldn't you go find mediocre comics with 2 or 3 subs to aggressively support -- the sorts of people who will sub back to you and be more likely to read your comic in return out of gratitude, but don't threaten your ranking?
And that tends to be exactly the behaviour I see from the few folks who do fall into that Threatened Mindset. Those are the folks trying to get sub-for-sub and insisting that if they read your comic it's impolite for you to not also read theirs.