Tools that agents have access to are the agent's body. Without them, they can't do anything.
For example, an agent without an ability to extract individual functions and check them in isolation, respecting the AST, has a hard time simply re-ordering and re-grouping the functions in a large file.
Even a frontier model struggles with this. In the same way that you would struggle to navigate the ocean without a sextant, or struggle to join two pieces of metal without a welder. Without tools, intelligence doesn't get you much in practice.
Of course - eventually agents will probably "craft their own tools", all the time, instantly. Many times they already do this, ad hoc bash/pythong/perl (or even sed or awk) scripts to do large replacements, or mechanical changes.
But these kind of thigns are still blunt instruments. Not exactly Switch watches or tooling with some elaborate regex and string replacing. If you give AI better tools, you give it better powers. And that's the power it needs to help you. At your goal.
For now, AI is all about the tools. Maybe when we have AGI, tools won't matter so much. But for now, an agent's tools really define the scope of its capability. I think a lot of money could be made with agents that figure out how to provide a complete "tool body" for agents (for a given domain) to make them really kick arse.
All that intelligence won't go a long way, unless you give it a way to express itself clearly.