WCQ lost not only just because of bad mentality, but because his strength and weakness has been exposed:
+ WCQ Strength: very strong serve/service game. He will try to suffocate you in first 3,4 points. His game is based around strong 3rd ball and strong BH flick receive. But if you could return his serve well (especially his hidden hook serve), it becomes a lot easier because his rallying game is not extremely dangerous like ML or FZD (in the words of Yukiya Uda who faced him in WTTC). Opponents now have studied his serve better and also limit his dangerous BH flick more with serve to FH (Truls in Olympics) - which means his game is a lot less effective now.
+ WCQ weakness: bad FH defense and FH counter against heavy topspin. Ma Long in World Cup Macao 2024 exposed his bad FH defense, and Truls, others run off with it - you see Anders Lind, 14 year old Iranian player Faraji, everyone targeting his weak FH defense. And especially, he's very bad with heavy topspin to his FH - he lost to Faraji, Anders Lind that way, and today again (!!!) can't seem to fix it. Truly not understandable, because top players are EXPECTED to know how to counter that. Kallberg today just spams heavy topspin to WCQ FH - then comes WCQ mistake / weak ball back. Same blueprint Anders Lind/Faraji used, yet no adjustment/improvement from WCQ. Just crazy to see.
Mentality plays a part, but if you lose 11-5, 11-6 then it's all tactics/techniques. His game was based on something easily decoded (serve/receive), and you could see it here. Coupled that with a deadly weakness (FH defense), it's just a no brainer why he's been losing so much.