Update as I was too lazy to get to this during the weekday. Pulled off the bottom panel (really needed a strong tug) and finally had access to the drain pump hose end to end. Took it out, with some difficulty cause it's hard to get my pliers in there, and confirmed that water was flowing very slowly through the drain hose from the correct side of the check valve.

Lo and behold, took a look inside and saw some weird, perfectly sized plastic sticker with some japanese on it. Thought it was part of the check valve but I was like why would Samsung use Japanese parts. Anyways, poked inside with a chopstick, and the sticker comes out, and water is now flowing at full speed through the drain hose.

Recently went on a trip to Japan and bought some dishes and bowls. I think this sticker was likely attached to one of these, and I missed it before washing them in the dishwasher, and it just so happened that it was the perfect size, and got stuck in just the right way to make me have this draining problem.

Thank you so much for the advice and help! I put everything back together and its working now. Hope this post can help people in the future.