I thought The Goal was more generally applicable. Its core idea ("theory of constraints") is described in terms of a factory floor where different workstations have different throughputs/latencies/reliability; you could apply that to a diagram of a distributed system [0], CPU [1] or server [2].
Phoenix and Unicorn project are essentially The Goal applied to software development. Reading The Goal first helped me get more out of Phoenix and Unicorn, I think. All 3 are great.
There are some excellent sequels to "The Goal", especially, "It's Not Luck," which goes on to take the theory into product and market design. It overlaps somewhat with Christensen's work on Jobs to do.
I've found lots of value in looking at all kinds of systems with this lens, though, like all things, it helps to not overdo it.
I feel like it would make a great movie a la The Big Short.
The academic paper in the appendix is super useful as well.