Legends of the Arena has a great story, that isn't as dark as Reborn and Rejuvenation, nor as difficult. The characters have their own unique personalities and the dialogue is quite witty. I definitely recommend it. It has a good amount of content, with about three episodes left to go before the story's done. There are some plot elements I'm really curious to find out the truth about, like the identity of a certain mysterious antagonist, and what does the protagonist have to do with all of it.
Pokemon Apex is difficult. It has level caps, restricts the number of Pokemon you can have in your party, and makes Pokeballs hard to get. The base stats and movesets of weaker Pokemon have apparently been modified so they are as usable as the stronger ones. The story seems interesting, but the demo is very short part of the the overall game.
I recommend Pokemon Alabaster if you haven't played it. It offers a great story, interesting characters, and a lot of choices. You can even choose what side you're on. Currently it has three badges and the level cap is somewhere around 44 I think. The starters are rare mons that are powerful when fully evolved but difficult to play with in their early stages. The gyms center around a theme and not a specific type, and they are pretty difficult. Alabaster is good, seriously.