why do you think agents you make yourself will be better for you? integration with tooling that you prefer? your local dev setup built in?

curious as i haven't gotten around to writing my own agent yet

All of the above at exactly the token cost that it requires for you.

Anything general is always going to be worse for specific use cases, and agents from these big providers are very general. They'll spend tons of tokens doing things that you might not need, including spend extra tokens on supporting MCP, etc., when you might not even need that.