Seeing all this Kuroto discussion really does reinforce for me that 90% of post-show content for any Kamen Rider show is just not good.

Unfortunately true.

Probably not. It can be hard to get back an actor that was on Kamen Rider four years ago, much less forty.

In Geats, the main current DGP roster here seems to be able to be compared with one another (other than Ginpen), both their similarities and contrasts at once.

Ace Ukiyo/Geats:

• To Keiwa: Both are the leads of the shows, but Ace's the kitsune, mysterious, hypercompetent experienced player, confident, deceitful, and famous celebrity to Keiwa's tanuki, ordinary man, weaker inexperienced player, self-doubts, straightforward, and unemployed.
• To Neon: Both are celebrities who longs for familial love, but Ace's knowledgeable about the world to huge degree (considering his age) and wants to find his mom who's missing, while Neon can be naive and out of touch and wants to run from her mom who she lives with.
• To Michinaga: Both are DGP veterans, but Ace doesn't directly talk down to others despite his arrogance (though he can give condescending pity to Keiwa) and is tactical and levelheaded against problems, while Michinaga directly talks down to others (like dismissing Keiwa and Neon as extras) and brute forces his way to any problems with anger.
• To Kanato: Both are the Riders who are the most concerned about the world's state, but while Ace keeps moving forward and opts for others to do the same, Kanato's stuck in the past that he's constantly miserable regarding his accident.
• To Morio: Both can pass off as helpful ally to others and can use dirty methods, but Ace can put a self-serving, profit-oriented facade that covers his compassion and tricks players equal/ahead of him, while Morio puts a friendly and easygoing facade that covers his opportunistic actions and can sabotage helpless players.

Keiwa Sakurai/Tycoon:

• To Neon: Both are DGP newcomers, naive and has been tricked, also grows more backbone later, but Keiwa's an everyman who is orphaned but has good relationship with remaining family, while Neon's a celebrity who has complete family and poor relationship with them. Their Boost debuts respectively are Neon dominating against mobs, and Keiwa failing against the final boss.
• To Michinaga: Both are Ace's primary rivals (as for ep. 7 for Keiwa), but Keiwa is team oriented who insists others working together to fight Jamatos, while Michinaga is a lone wolf who views every players as enemies.
• To Kanato: Both seem to be DGP players who care the least about winning the game, but Keiwa focuses on helping other players, while Kanato focuses on bringing other players down.
• To Morio: Both are 2 of the most outwardly cordial Riders, but Keiwa genuinely cares about others whenever they're up or down, while Morio only cares about those who can benefit him (including the way they utilize rescue points) and can turn on those useless to him.

Neon Kurama/Na-Go:

• To Michinaga: Both are the players Keiwa helped by giving Boost Buckle away, but Neon is team oriented in playing the game by trying to team up with players, while Michinaga is lone wolf who rebuffs other's helping hand towards him.
• To Kanato: Both are infected in Zombie Survival and has bleak past, but Neon tries to prevent her infection from spreading to others and she passes the round by being hopeful and not giving up, while Kanato wants to spread his infection out of spite and he got eliminated by succumbing to despair.
• To Morio: Both are 2 of the Riders most associated with wealth, but Neon had herself being victimized with Kurama's wealth being used as her ransom, while Morio's the offender with him embezzling money at the illegal casino.

Michinaga Azuma/Buffa:

• To Kanato: Both are 2 of the outwardly rudest DGP players and has a wish of crushing a group, but Michinaga fights exclusively close-ranged and his wish is limited (only to Riders), while Kanato fights exclusively long-ranged and his wish is all-encompassing (entire humanity).
• To Morio: Both are Special Ticket users in Concentration and proclaim they'd do anything to win, but Michinaga's typically honest and plays fairly, while Morio frequently lies to cover himself up and can cheat.

Kanato Sumida/Da-Paan:

• To Morio: Both are the villainous Riders among the current DGP roster, but Kanato is rude and hostile to others and is more over the top to exterminate entire humanity, while Morio puts a friendly facade and is more grounded to 'only' try running away from his crime responsibilities.

As a matter of fact, we have an example of Hiroshi Fujioka who came back repeatedly. And in general, just the same Zi-O was able to return quite a lot of actors, including those from the series 20 years ago (and even Norider from the 88th)

By the way, I think that Geats is a good confirmation that the concept of the secondary rider is better left in Heisei. In the show, the title equally suits Keiwa (essentially the protagonist of the story, who is mostly watched by the viewer, favored by fate and the first of the newcomers to get his strong form), Michinaga (literally the second rider to appear on the screen and the second most powerful after Geats) and Neon (the second in the show used by Boost and was the first to team up with the main character).

it's Kamen Rider Blade time baby

Maybe something’s changed since I stopped watching, but isn’t Tycoon essentially a POV character like Gatack? That seems to easily pin him as the secondary.

Pretty much.

But also, there's a real simple answer as to who's secondary and who's tertiary that I will always point to.

Oronamin C Commercials

Those usually show us who the main trio of Riders are.

Mostly cause last year was crazy with people being like "Demons is the Secondary" then Evil/Live happened, and they're like "Okay Demons is the tertiary" and because Jeanne was pretty much P Bandai, everyone was arguing over who got precedence over the other so I just decided to wait for Oronamin C to decide (even though it as obvious) and we got Revi, Vice, Live and Jeanne as the main Riders in that commercial.

Well yeah, but there’s also Toru Okazaki, who hasn’t appeared as Amazon since the last episode of Stronger and doesn&t act at all anymore.

I’m not saying we couldn’t see Sougo come back in 37 years, I just wouldn’t bank on it being anything more than possible.