Yes, without the side stories there are too many open questions.
I don't know if you wanted to describe the end without side stories or if where you read they didn't have the side stories. If the later is the case, there actually are three side stories (another one will be added after RAIYC or next year), two of them kind of continue the main story.
It was the same earlier this year with DMIYC, it felt much better after the author released extra 1, ~ two weeks after the main story ended. The ending of the main story was too sudden.
And Grayson can be a big asshole, but he isn't really a villain. He did cause trauma on Chase, but it wasn't intentional. He isn't even aware of it at that point. That doesn't make it any better for Chase, but that might be the reason why it felt unsatisfying for you that "Grayson was just there" and wasn't dealt with as a normal villain would be.
I think it will take quite some time. Not nearly as much as Remarried Empress, 19 days or Fate Makes no Mistakes (I'm talking ab a lifetime here) but there's still a significant time for sure. Maybe 2 or 3 seasons. About the recommendations, I'd tell you to look at this reading list I made on my profile "I felt THINGS". We may or may not agree on what good art is, but I can tell you I've been adding what for me has been the best of the best since around 2017. It's mostly BL (if not all) and you can find some more omegaverse in there too. I'd personally highlight "Nerd Project", "Our sunny days", "Perfect Buddy" and "Semantic Error" for you :)
I'll paste the link below:
https://www.mangago.zone/home/mangalist/2986348/
I'm here if you have anything to ask ^^
Yeah you're right. I was too disappointed by the end of the main story and felt discouraged to read the side stories, like I was robbed of a real good story. Now with my head a bit colder I might give the side stories a try. Note that this is the only story I've read from this author. I know about the others but they don't seem appealing enough to me so maybe that's why this one feels so incomplete. But anyways thanks for the insight <3
As I said two of the side stories continue the main story, you should read them. There are some things you most likely wanted to see in they main story that happens there.
As for the other Miller stories, it chronologically starts with the grandparent's story, which is dark.
The one of the parents, especially the extras which includes the children, helps understanding the situation of the family. You don't really understand it if you only see Chase perspective.
Grayson's story is the one I would recommend the most if you like stronger omegas and want to laugh a lot, because you're not prepared for Grayson's crazyness (he is actually full of surprises lol), Dane was certainly not. The couple is pretty even in power, because dominant omegas have an advantage over dominant alphas, but in addition Dane is very tall, physically very stong and trained in combat. While Grayson is more of an ultra dominant alpha, he is stronger than a normal one. Josh and Dane are friends, so Josh is involved in that story too. The Miller parents are also involved in that story.
But as I mentioned, this one also needs the extra which was released, because it directly continues the main story.
Nathaniel's is still in progress.

it was such a disappointment. It was interesting and all until everyone started getting shot & hospitalized or kidnapped and then Grayson was a villain that was just... there I guess. The secret pregnancy thing turned absolutelly irrelevant: the three of them (Chase, Josh and Pete) were at an amusement park and then suddenly were at some big abandoned place with wild dogs? And Chase had a big moment where he ignored the dogs and saved Pete and then Josh was like "it's your child too. And btw you never had unconscious sex with a dog Grayson was just mean and lied." and Chase basically ignores Pete and goes all about the dog's issue. Next scene is a huge timeskip to show they lived a happily ever after. And that's it. Such a lack of flavor.