I find the percentage-based swipe input distracting. I kept thinking how the exact number is going to affect recommendations and how that is measured relative to my previous inputs.
Consider showing two concepts next to each other so that swiping chooses one or the other, and swiping up chooses both.
Hmm, yeah, the swiping UX seems to be pretty tricky to get right. Initially I didn't have the percentage but some early testers highly recommended I add it for two reasons:
1) They couldn't see well and found the addition of the percentage was helpful in clarifying their swipe value.
2) It made it more obvious that the magnitude of swiping mattered, as opposed to swiping just being a binary yes/no option.
The two concepts idea is interesting. I'll have to think more on that. I think it might be tricky to implement though, because not every topic has a natural converse.
In case you're interested, I created a quite long time ago a small example of a library doing this.
https://github.com/dgellow/react-tinderable/blob/master/src/...
The code is really old and out of date, and was just a quick experiment, but that may give you some direction if at some point you want to try out that kind of user experience.
Unfortunately the demo link doesn't work anymore, but it should be quite easy to run locally.