The CEO/C-Suite/Board is responsible for the behavior of the company; they set the rules, and steer the "ship." They decide what money is allocated where.
I'm not sure who is glorifying mediocrity, that's an odd one.
Close, but actually large PE firms call the shots. A small number of them control most tech, that’s why all these companies look like cookie cutter copies of each other.
PE firms do exert massive influence, but they aren't really the day to day business drivers. Even including the board is tenuous. Board members are often out of touch with the business and just rubber stamps - look how well the OpenAI board performed. If you think Sam Altman should have been fired, they failed, and if you think he should not have been fired, they failed.