I almost wonder if they read and were incensed by this particular conversation, but someone went and simply asked the author who won.
https://x.com/i/status/2060036713326756025

It was Youmu. That's why she gets called -sama (though I also thought there was a chance of Yuyuko just being nice/messing around). The 6-sou Youmu discards in ch. 37 is actually in that later game against Rumia, and what she cut against Remilia is "a secret".

That's what I've been saying! Yuyuko calling Youmu -sama was a big hint, I knew it!!

I'm surprised the author was willing to give a direct answer, since authors tend to like leaving things for viewers to interpret (or figure out themselves like in this case), but I'm not complaining. Youmu won!!

Remi won the title of Champion. Youmu still got the league title of Self-League and "has" to be called -sama by others. The Ending isn't confusing and you don't need to "interpret" anything if you understand mahjong. Here's a little breakdown.

League Matches:
- The purpose of the Four Senses Zenith Cup is to decide who gets one of the four titles associated with the four leagues (Self, Other, Earth, Heaven) and gets to be called -sama. (ch. 03, page 10-11)
- The accumulative scores from each league decide which three players in the league get to play the current title-holder, the top two of these matches go to the semi-finals. (ch. 18, page 11)
- Youmu and Akyuu (Self-League) won against Shou and Doremy to enter the semi-finals against Yuyuko and Satori (Other-League).
- Marisa and Tewi (Earth-League) vs. Remi and Nue (Heaven-League) made up the second semi-finals.
- Both Self-League players (Youmu and Akyuu) entered the finals.
- Marisa (Earth-League) and Remi (Heaven-League) joined them from the second semi-finals.

Simply by virtue of entering the finals you are already one of the four best riichi players in gensokyou and get a title from it. Presumably the one from the league you came from, even though this year there seems to be no Other-League player who made it. (Maybe Youmu or Akyuu get a different title so the cool "Four Senses" introduction like in chapter 3 still works next year?)

Breakdown of the Final (South 4) Round:
- ch. 36, page 21: Remi calls Pon, disrupting the regular turn order. This screws up the two Riichi hands from Akyuu and Marisa.
- ch. 36, page 24: At the end of Turn 13, we see Remi with two Honor Triplets, South Wind (Nan) and Green Dragon (Hatsu), and one 9-man triplet. She also has 1-sou, 3-sou, 5-sou, 7-sou and 9-sou. (sou is bamboo). She has to discard, and chooses to cut the 9-sou.
- ch. 36, page 29: We're in turn 17 and can see Remi's discards. The 9-sou she discarded on page 24, followed by a 4-sou, which she drew and discarded, a 2-man, which she drew and discarded and a 3-sou, which she had in her hand, so she must have kept her draw! If you reconstruct what Remi's hand must look like now after these discards, you know what's lurking!!!!
- ch. 36, page 30: Youmu has to decide between discarding 4-pin or 6-sou. She thinks 4-pin could help Akyuu finish her Riichi call (it would not! but she can't know that). Noo! Youmuu!! Don't discard 6-sou! What if Remi got a pair on her last draw?? But we have to wait for the next chapter to find out!! T_T
- In chapter 37 she discards 6-sou and Remi calls Ron. Confirming she got the pair. Oh well, it was a guess, I guess. What can you really do against fate?
- ch. 37, page 16: shows Remi's final hand in case you weren't thinking along last chapter. It is now clear the tile she kept in favour of the 3-sou was another 1-sou! (Making a pair of 1-sou) and Youmu's discard (6-sou) fits perfectly between her 5-sou and 7-sou, making it a sequence. She now has 1 pair, 1 sequence and 3 triplets. The fact she called Ron on the last possible discard makes it Houtei (instead of Haitei as in the translation) and therefore a winning hand worth 6400 points.
- At the End of South 3, Youmu had 39300 points and Remi 25600. Youmu now has to pay Remi 6400 points. And Remi gets the 2000 points from the two unresolved riichi bets from akyuu and marisa (1000 each). This brings Youmu to 32900 points and Remi to 34000! Just 1100 points more, just like Patchy said, but still a win.

So Fate won once again, but at least Youmu, Akyuu, Marisa (and Remi) got their league titles and have to be called -sama by other mahjong players, so that's not nothing! On page 19 of chapter 37 we can see Youmu trying to explain her loss but Yuyuko doesn't care about that. She's just happy Youmu progressed so much to fail just short of Fate herself. What a nice ending.

Personally, I would not have minded for Remi to just have been an insanely good player with no tricks as insinuated in the last couple of chapters and for Youmu to win in the end. But this ending is a lot more Touhou, I think.

I lost access to my throwaway account from back then ("TheTomEngine31"), so I might as well create an actual account for this. Anyway...

As far as I saw, nowhere does it say that reaching the finals gives you a title as being part of the four senses. You even admit in the same post that this interpretation is flawed by pointing out that both Youmu & Akyuu are from the "Self-League" and that there's no Other-League finalists.

Again as I pointed out, Patchouli described something that COULD have happened, not something that definitely DID happen. Especially with how you seemingly leave out the fact Youmu's had multiple options for her final move and did have a win condition.

"On page 19 of chapter 37 we can see Youmu trying to explain her loss" She didn't. You're literally putting words in Youmu's mouth. Speaking of the last part of the ending, the fact Yuyuko calls Youmu "-sama" is heavily implied if not confirmed to not only reveal the results of the tournament, but also was something the series built up towards from the start, both based on the author's statements on Twitter.

That's pretty important information and hard to ignore. Youmu won the title of Champion.