Hi and welcome to Wattpad!
The best way to get a critique is to find them through the Find a Critic thread. There are a lot of people who don’t always do their end of the bargain, so you can try to find those that have simple payments like a follow or adding their book to your reading list. But if you can’t find someone to do it, post your own advert. Of course, this will mean that it changes from finding a critic to a critique exchange (you do theirs, they do yours). But to make sure it happens properly, you want to add in that they have to do their side of the bargain first before you do yours. This way, it’s not like cheating. You know?
The rate threads aren’t all that great at finding feedback as, like you said, are mainly one sentence stuff, but I do recommend trying out the critique threads in the Improve Your Writing club.
Most critiques I’ve gotten are very helpful. They usually do a couple paragraphs for the overall story and other things regarding mistakes, and it is well worth it. I have, however, experienced some half-assed critiques or too-opinionated critiques that weren’t all that helpful, but I hardly experience these. I think the last time it happened was like a year ago, so… it doesn’t happen often. But two of the major ones that came to mind was some guy who didn’t even read my story (or it seemed like it) as they were like, “Who is the character? You need more character development.” Even though the name of the MC was in the chapter… like five times. And plus, if that wasn’t enough, their name was on the summary. And they never explained why I needed character development or where I needed it. That was my half-assed experience.
Another person was like, “Why did he ask her if she’s okay? Obviously she’s not fine… her fiance died! I think this needs to be rewritten.” Even though what this person was referring to was a normal, human interaction. Have you ever been sad or crying and someone asked, “Are you okay?” Because I have, even though it’s obvious that I’m not okay. And that’s what happened in the story… xD The same person also told me that the last name of another character seemed too forced, even though I’ve met people who have “too forced” last names… Haha So that was my too-opinionated experience.