A CEO of a large company and a CEO of a small company have different work priorities.
Yagoo delegated upper management for all things relating to the projects and well-being of talents.
What's needed is a direct channel between talents and Yagoo, which is not possible since Yagoo is busy with a categorically different type of work that only he can be trusted with. He just can't afford it, anymore.

If it continues like this, Hololive's internal structure is going to stagnate forever.

There are some very niche solutions that are viable, however.

Large corporations rarely have something called "Ombuds Office", which is a self-investigatory conflict management body of a company.
When a complaint arrives from a talent, that office will investigate a decision or conduct to ascertain whether it may be overruled or the suspect met with reprimandation.
It's basically there to keep negligent, malignant or powertripping high-rank employees in check.

Another solution (that I have never seen before) is a team of veteran executive assistants situated just below Yagoo.
They may serve as arbiters of talent complaints and may overrule decisions based on a talent-biased consideration of their interests vs. the immediate well-being of the company.
This team would require very competent and very trusting employees, though. Additionally, they would be considered adversaries to upper management, which could also be a problem.