There's a lot of overlap, and you could certainly use "pragmatic" in the two example contexts I gave. The differences as best as I can sum them up are:

- "Pragmatic" can also be used to describe a person (a pragmatic person) or a mindset (a pragmatic approach to a problem.) "Expedient" isn't used to describe people.

- "Expedient" usually acknowledges the existence of a higher or more demanding standard that the solution does not meet, admitting that the solution is not perfect. You might choose a word like "pragmatic" to praise a solution with known shortcomings, but it doesn't imply known shortcomings as strongly as "expedient" does.

- "Expedient" can be used euphemistically. ("Pragmatic" can, too, but not nearly as often, and not as harshly.) "They took the expedient route" might, depending on the context, mean that they did something lazy or unethical because it was easier. The euphemistic usage is common enough that for some people it has an overall unsavory flavor, but I don't think it's tipped over into the euphemistic usage being the assumed one.

"Pragmatic" connotes a choice that achieves a goal by practical means, possibly sacrificing some desirable features that are challenging to achieve.

"Expedient" connotes a choice that achieves a goal quickly and conveniently, possibly by sacrificing some important but difficult features, and incurring some undesirable costs or consequences.

So they're similar, but not identical. A pragmatic choice might be improved when you can afford it. An expedient choice will probably require some cleanup afterward.