1) Culture must evolve with other elements of the company and at certain stages of growth and transition a company may need to intentionally hire to provoke and shape cultural change. Your change agents will be getting flak from many directions and your role may be to cover them and defend their advances.

2) This sounds like entrenching the status quo, risking stagnation. Every company I've ever worked at had some enshrined and virtually unassailable principles and practices. Celebrate the heretics and iconoclasts. It takes a strong internal center to speak out against groupthink and cultural norms. Make thoughtful challenge to the principles a principle (i.e. it cannot be a notwithstanding clause that supports blanket circumvention of other principles). Institutionalize periodic reviews.

3) The company and culture may change out from under some employees. An amicable and blameless split is best, including not blaming yourself. And every new hire constitutes some risk. So much hiring practice aims to minimize that risk without measuring or understanding the cost. It's easy to see and feel the effects of a bad hire, almost impossible to perceive the lost opportunity of a false negative.

Sometimes failure was not avoidable and there are no lessons to be learned to avoid similar situations in the future. Move on quickly, don't dwell.

4) Sounds like the Wobegon Corporation. Supporting cultural evolution is tough, often evolutionary and glacial rather than revolutionary and seismic. Your star performers in a micro-organization may be ineffective at the next level of scale because success then requires a different set of skills. Objective evaluation, effective performance and career management are tough problems made more so in a transitional company.

The culture that supported the company's previous stage needs to adapt for the next. Cultural change requires both people changing and changes in people. Elements of a company's culture will not scale. In organizations of which I've been part recently I've been promoting organizational Agility (capitalization intentional) in which Agile practices are applied to processes and structures, which adapt in response to internal and external forces. Cultural lock in retards progress.

WRT OP, these changes are necessary to support the company's current and continued growth, and I would avoid ascribing sinister intent. The company is changing in ways that don't match your personal work style, in which case it may be time to ask if you can adapt to this new reality (which may mean changing role or function within the company, rather than simply letting momentum carry you forward in your existing position) or look for a different company better aligned with your sweet spot (and do so in a way that is a positive experience on all sides, and don't wait to the point where you are acting out of frustration).

Change means new opportunities, possibilities to be teased out of your current situation. If a role exists or can be created that better suits your strengths, have a conversation with your manager and propose some changes, even as an experiment, "What if we tried ....", with an agreement to meet on a set time frame and evaluate results and pivot or course correct.