People who are saying, “This series doesn’t meet my definition of ‘yuri,’” well, whatever—feel free to put forth that definition and make your argument.
People who are saying, “This doesn’t deserve the Yuri
tag” are simply mistaken about what that tag means on Dynasty, where it means that, at minimum, the tagged story contains a character who is in love with, or who desires a lesbian relationship with, a female-identified character in the story.
Obviously, Rio is that character in this story, when in chapter 9 she asks Matoi, “Why don’t we start dating instead?”, and then kisses her. Many people have argued that, in addition, the main plot contains enough yuri elements to deserve the tag in itself. That may or may not be so, but such a reading is not necessary for Dynasty tagging purposes.
Moreover, the author’s note at the end says unequivocally that they intend this to be a type of yuri story. Readers are certainly welcome to disagree with the author, but the authorial statement further reinforces the appropriateness of the yuri tag for this series.