Adding on to other suggestions, if you're not aware of Ventoy it's a very handy tool. Using it you can have a USB drive with several live images on it which you can choose at boot time. Great for quick testing, just drop an ISO in a folder!
Me too but I might replace with https://www.system-rescue.org/System-tools/. Gparted live is really hard to customize and doesn't run as root, makes no sense for a rescue tool. SystemRescue also seems to come with something similar to rEFInd to boot broken systems...
I maintain my own Debian-based live image. It's a general-purpose desktop, with a good amount of diagnostic/troubleshooting tools. It's quite easy to build your own using different package lists or default configuration, etc.
I've gotten good mileage out of just an Ubuntu live image. If the network is working you can install packages via apt like normal, but they include a lot of the basics already.
Kali was built out as a penetration testing distro, though it does contain some diagnostic tools.
Not a bad place to start if you're used to Debian, but it is a rolling release so it may break unexpectedly, or have new bugs introduced with each update.
A persistent USB with just Debian could have all the same tools installed but have a longer support scope on releases so you don't have to update daily (bleeding edge) which is nice to reduce read/writes to the flash drive it's on.
That being said, I keep a Kali live image (persistent) but thats becauae its home - my first introduction to Linux was 5 minutes with Red Hat, but aside from a brief intro in highschool, I really started with Linux in Backtrack, offensive security's predecessor to Kali.
Thanks for your opinion, but you don’t get to decide what I need. I wanted a simple distro that I was familiar with, so that I could teach it to someone with basic computer knowledge. Teaching how to use a terminal was outside the scope.