For those who have an installation of LaTeX: It is pretty easy to use LaTeX for this.
Without looking it up the arguments/syntax, how do I do "join page 2-3 from PDF A with page 7-23 from PDF B"?
If it's more than one CLI invocation, easy to remember/find in the shell history and less than 80 characters long, I'm not sure I'd call it easy :)
pdfjam PDF_A.pdf '2-3' PDF_B.pdf '7-23' --outfile joined.pdf
I'll admit that I had to look it up but that only took about 3 minutes (it's an example in the readme).