The feed you see when you're logged out or not following anyone serves as the "main page" equivalent, and it's just as susceptible to corruption as reddit's /r/all. For years people said the same thing about reddit: the easy-content corruption didn't matter because you could just follow different subreddits. But even among my followers, it seems people vote more for agreeable short content rather than long content.
I think that in a lot of ways Hubski's architecture is more akin to Twitter than it is reddit. Nobody goes to twitter to see a main page. Right now we have a very small site but if it were to grow those global pages would become pretty meaningless IMO. You would have to construct your own feed. You could seek out those posts you deem high integrity and follow others that feel similarly. Is this going to eliminate the occasional puff piece being shared in to your feed? No. We're humans, we like candy even if we say we only eat healthily. You been on Hubski IRC lately? I've been stopping by randomly but nobody is around.