"have to hire"
No, they don't. I'll let you in on a little secret. There's these things called MMA gyms. You pay a flat rate and train with the wrestling coach, the BJJ coach, the striking coach. They are not hired and paid individually
All the shit you just mentioned? That's excessive and not necessary
This has got to be the dumbest post I have ever read in my entire life.
MMA gym training is fucking trash!
You are stuck with cookie cutter trainers and you have to drill the same generic move and combos over and over again. There is a reason why MMA gyms have to recruit wrestlers or other fighters from different style and that is because at the end of the day, MMA is just Muay Thai with jujitsu in a room filled with people drilling the same move over and over again.
Real boxing gyms, grappling circles and dojos/dojangs:
You work with a mentor to establish a foundation, after that you learn a primary move and then you develop a game that is revolved around your talents. The mentors, coaches, sensei's will work with you to understand your individual needs. To see if you have fast or slow twitch muscle so they can determine if you are a volume fighter, grinder or an explosive fighter.
In the mid-2000s, the talk as "In 10 years, no one will come from a wrestling background or a jujitsu background, everyone will be an MMA fighter from the start, this is the future!"
Time skip to 2022 and the ONLY fighter that fought in the UFC who started off as with MMA was Rory Macdonald. That is it! No one else comes from MMA. Khabib, Colby, Usman, Khamzat are wrestlers, Israel is a kickboxer, Conor is boxing/TKD mix early on and Francis focused on boxing since he wanted to be a boxer originally.
Now to address your final point, if you hire coaches individually, you can develop SPECIFIC move set and specific techniques in grappling and striking. You can truly mix and match techniques as oppose to just hitting the same redundant Muay Thai combo in every MMA gym. Hence why MMA gyms suck!