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.

Yes, I have to learn things the hard way lol.