It's not the model. It's the missing context.
Agents make assumptions when they can't see your product. Without the decisions, constraints, and priorities your team already settled, they wander the codebase, guess, and get reworked three to five times before a feature is right.
Brief feeds that context up front, over MCP, before the agent writes a line. Fewer assumptions, fewer cycles. The same token budget spent deliberately instead of spent wandering.