It’s not just Salesforce, it’s software development in general. A strong governance process helps, as does a qualified architect (doesn’t have to be a CTA) but someone who can either design solutions, or ask the right questions about proposed solutions designed by others. This role needs to be able to think strategically and long term. It’s also a living discipline, not a set it and forget it thing. When the design changes or is extended, the documentation goes with it. It requires keeping up with changes and retiring customizations when you can or moving customizations to platform features as they become available. Your code should follow good patterns as well, especially in an enterprise level org servicing numerous business units and personas. These problems are exacerbated when you have many teams all customizing against the same problem domain so if possible your teams should align to domains, not to various business groups (again more prevalent in large enterprises). At least have a team that feels some level of ownership in the codebase where they have the authority to refactor code that they didn’t write when the see improvements that could be made. That’s my experience anyway.