Let's be honest, none of the side characters are particularly interesting.

Rinko is basically completely useless, despite clearly being a powerful and intelligent woman to have the career that she does have.

Shunpei is kind and childlike but he still basically achieves nothing, except when it's crucial to the plot that he does.

And Koyomi seems to exist only to give the anoraks something to shout kawaii at their screens for.

on OOO episode 30, ok so i dont wanna know yet but please tell me Maki will quit stalkin and thinkin Chiyoko is his dead sister? soon!

But that doesn't mean they can't be interesting.

Rinko is a detective. That alone grants her so much possibility if they utilized her more, like during the Phoenix arc.

Shunpei...

Koyumi isn't a human. There's so much they could do with her beyond waiting until the last 5 episodes for some kind of "Shocking" twist.

But even in the Phoenix arc Rinko was useless, I know he is a super powered monster but Rinko would have had some combat, fitness and negotiation training. Instead she bumbled herself into getting captured, was extremely gullible making incredibly stupid decisions and showed absolutely no thought before she spoke. It was nonsense, if someone this incompetent is a detective then I'm surprised that whole city isn't burning around them.

And Koyomi's backstory was really interesting, but she was a massive arsehole so I didn't care. However once they softened her, it made her completely irrelevant as she now just stands in the background pulling constipated facial expressions and gushing over Haruto while she touches his crotch as the belt screams, "Please! Please!"

Anything that gets the side characters off their asses and doing more than shining Haruto's shoes.

I'd rather they just cut them out entirely so we could focus on our Riders, their battles and the villains they face.

I wouldn't.
Haruto can't sense Phantoms. Only Koyumi.
Rinko has the connections that sometimes proves vital.
Shunpei helps keep the gates from going full retard.

Adding that Nitou has no connection to the Gates (Haruto doesn't want anyone to despair, giving him a slight connection. Nitou just wants to eat and isn't willing to let others die, but he more often than not just stumble around), and you can't just focus on the two guys who fight just because they're the ones who fight.

Give Haruto that ability then, take Koyomi out if you aren't going to build anything around her one novelty.

Now they have that Agent Zero guy on their side, Rinko's original benefits are basically no longer needed.

Shunpei...

And yeah, I think Beast is the clumsiness of the show at its finest, he has an interesting backstory and cool powers but he just kinda...appears, feels like he has come from another show entirely and although the stakes are high for him the show downplays it to such a degree that it feels almost pointless.

I'd rather focus on the fighting than side characters who are meaningless and waste my time.

I'm getting pretty close to catching up on Wizard now so can I get some suggestions as to what series I should pick up next?

Basically I'd love another series like Wizard, just with less filler and pointless side characters. I also despise the goofball toku comedies, so if there is a proportionate amount of that don't bother suggesting it :lol

Also for the record I've seen W, Kiva, Wizard and Dragon Knight.

Try Kamen Rider OOO.