Most developers are currently building MCP servers that wrap a 3rd party or wrap their own service. And in this case, they are still at deciding on the tools in design-time, not runtime.
Also I want to mention that both Cursor and Claude desktop don't support dynamic toggling on / off tools within a MCP server, which means users can't really pick which tools to expose to AI. It exposes all tools within a MCP server in current implementation.