The art is great, the world building is varied and inspired, and this story's equivalent plot of fighting the demon king is honestly well done, with a lot of amazing character interactions and interesting characters.
But there's one major flaw rooted in the promise this story makes to the reader, and unfortunately this flaw is central to the storytelling mechanism that progresses the story: The author keeps regressing the progress of the relationship of the main character and the first wife.
The story makes the following promises to the reader: The main character will gather a harem, the main character will learn to love them all deeply, and this deep connection will enable them to defeat the greatest foe the world has ever seen.
The author decides progress with the other wives will only happen after enough progress is made with the first wife. But progress isn't allowed to be kept with the first wife in several ways that show the author's hand is so heavy I'm surprised earthquakes don't show up with every keystroke. It's that obvious.
This relationship reset causes the main character to intentionally ignore his other wives, which increases the tension, but it's hard to read because of how artificially, implausibly and nonsensically the relationship with the first wife is reset:
The other wives want their turn and are forced to wait; the more they wait the more they get competitive. This tension causes the first wife to feel insecure, causing the main character to always hold back until she goes so far he takes a manly stand to show her she shouldn't be insecure, and then progress is made.... And then the author forces their relationship to regress, but with the caveat of the other wives becoming more impatient and competitive as a result, making the next bout of insecurity worse.
And this situation is made worse by the fact that:
THE PREMISE OF THIS STORY'S PLOT IS FOR THE RING KING TO INCREASE HIS POWER BY INCREASING THE DEPTH OF HIS RELATIONSHIPS WITH THE RING PRINCESSES.
The promise this story makes is opposite to the progress the main relationship (in a harem) makes. The author refuses to progress the main relationship in a natural or believable way. It's awful. It feels like I'm reading the same nonsense reasoning as the Hegelian dialectic... and now that I think about it, that's kind of what this is: I want two opposite things at the same time, and so I try to force them together until some magical compromise or evolution is discovered.
For this story, the opposites are harem and monogamy (where a person having one automatically disqualifies them having the other). The author seems to want both at the same time, so they write both happening at the same time and hope a compromise or evolution is discovered along the way. And the results?
Plot holes, an underpowered MC, and tens of thousands of extra deaths that didn't need to happen. Just like the eventual results of IRL Hegelian dialectic, interestingly enough (over a hundred million deaths, really; if you know, you know—it's a long explanation of how, but if I were to give an oversimplified hint: "Struggle session, anyone?").
Basically, since the relationships of the main character and his wives is required by the plot, and the author keeps refusing to fulfill those requirements, it means most of the actually good writing happening outside of said relationships is wasted.
Honestly, the pretty art and the desire to see how this train wreck unfolds is why I'm still reading this. But things keep getting worse because in later chapters...
The first wife's younger sister shows up.
This literary means the main character didn't have to be the main character, his love interest didn't need to be part of the main plot, and is the second (technically first, but retroactively made) time the author has forced a character to act in ways they shouldn't have that affects the plot.
This author is retroactively adding plot holes to try and resolve their story. This feels like another case of a great artist that doesn't know how to write. They certainly have a place in the industry as an artist, but not as a writer. And with all due respect, I think that's normal.