Big agree, especially if it was something that was presented to readers as well, I think a tier system would honestly do more harm than good? My gut reaction is that it would be even more of a deterrent for people than the current "popular/trending" system
Like, right now you're at least either on one of those lists or not. Everything else is kinda fair game. Comics that are poor quality still don't get as much traffic and those that are better quality still get more but it's flexible, I guess?
Whereas I'm envisioning if there were, say, Tiers S-F. If you can sort by that then... I would personally probably never look below tier B or C, personally, unless it was a direct recommendation from the author or otherwise. I'm given a preconceived notion as a reader that those lower tier stories exist but are clearly not worth my time. I feel like would-be low tier comics already have a hard enough time without having a big ol' "Kick Me!" sign slapped on as a first impression as well 
The only way i could see this being useful is if it were a dashboard exclusive feature or something. Similar to the follower milestones we have currently, you could have a little tier rating with parameters to move up and the promise of getting featured once you reach Tier whatever. That would seem kinda contrived still, but at least it would give creators something to work towards without tainting reader impressions? I dunno.
I'm team "improve filtering/searchability", personally. The ideas in this thread about multi-genre filtering, or putting higher emphasis on series tags (but also would have to be coupled with Tapas promoting to readers "hey, searching is a good option!" because right now it's a browse-oriented site) would be generally beneficial. Sure, the premium "Fantasy / Action series with tags "magic" and "elves" would still be higher up the search results than joe schmo's, but it would make the overall list smaller and that's significant for discoverability.