The DCEU has been part of that discussion. Shazam 2 and Black Adam flopping is prove. XCU never existed, X-Men never had a cinematic universe, fox just made movies of the series and this franchise has been officially dead since 2017. Had Disney not bought fox, fox would have carried on with their random mixed bag movies of the good and bad which will never have caused fatigued since the genre will still feel more like the science fiction or romantic genre with bad and good movies.
Its the cinematic universe movies that are making the genre fatigued not self contained films. I would have predicted that a hard core X-Men reboot under Fox of good quality would have been fared a lot better and felt more fresh than any of the predicable MCU Disney X-Men films.
DCEU may be part of the fatigue discussion but this does not apply to the entire DC universe since DC has other projects not tied to the DCEU that are more applicable to the romantic or science fiction genre as well. I hope Batman never shows up i the James Gunn reboot universe.
MCU and DCU types of movies is what is fatigued. other movies like Into the Spideverse 2 and The Batman 2, I don't see as part of the fatigue problem.