Actually I own several hammers which spark joy: a small mini-hammer which fits perfectly in my hand. A large sledge hammer which is entirely too heavy to be practical, but feels like wielding Mjolnir when I use it to break brake discs loose.
The real gray area is when you have some poor quality tools which you do need and use, and you can't yet afford to replace them with ones that do spark joy.
Yes, that dingy 'harbor freight zone' of joyless, but functional tools that would cost more than their utility to replace. I have found many tools I did not expect, can be rented at local stores. Its not like I need that brake tool every week to keep my home nice.
Living out of the sticks, the tool that brings me joy is the one that's already lying around in my workshop, and that I don't need to drive into town to buy on that once-in-a-year occasion that I need it.
Personally I try and buy tools second hand, as they are typically cheaper and of better quality than the new tools sold in hardware stores. And they can be resold for about the same I paid for them, making them free to own.
Apart, that is, from their alleged intrusion on my personal joy from cluttering my workshop. Which is rubbish - workshops should be exempt from this joyful thinking, they are places where you want to find that useful piece of scrap material lying somewhere - anywhere - when you need it.
I think what Kondo would say in this situation is that having those things sparks joy for you. You should keep the scrap materials, but try to organize them in ways that allow you to quickly see everything you have so you don't forget about or lose things.
One of her rules seems to be "Try to organize your objects in a way that each one can be viewed without having to move another". Pile is worse than a Box is worse than trays/drawers. Organizing your scraps by category and size would likely make them provide more utility to you?
But as someone with a cluttered workshop trying to figure out a good organization scheme, I may be thinking too much about this. Anyone have a quote from her about workshop/scrap materials?
It feels like you're arguing against something that isn't really what Kondo is offering, and she specifically discusses in reference to vacuum cleaners and screwdrivers (tools you don't need every day, but the frustration of not having is an "anti joy"). The joy concept isn't so rigid as delight in that moment, though it can be misconstrued that way.
What I think she would say about a workshop is that a well-organized (tidy) space, where everything has its place, so you know where to go when you need something, and where it goes when you have finished using it, is going to make you a happier person than having to dig through a toolbox/drawer/scrap pile to find the right tool or piece of wood.
In my experience, workshops are not devoid of joy, unless you work only on things you don't enjoy or find pride in, which seems unfortunate. My workshop memories are of my granddad making wood products of all sorts, my dad working on the car and various household projects, and my brother creating toys of various types (e.g. making our own cornhole set). The frustrations in the workshop were typically of not being able to find something I knew was there, but perhaps that isn't what you are after or expressing here.
The real gray area is when you have some poor quality tools which you do need and use, and you can't yet afford to replace them with ones that do spark joy.