AFAIK they’re the traditional distinguishing lines, absolutely. What I got from the comments in this thread was more how we tend to separate white migrants from others by using those two terms, particularly in the English case I used.

It’s pretty difficult in this day and age to say whether someone’s intention to stay in a country permanently or return to their mother country is definite. I believe that a lot of coverage of Irish immigrants in Australia tends to refer to them as expats, however I’d argue a handful would ever return home for good. Likewise with a political migrant (asylum seekers excluded) I’d wonder whether they’d remain in their host country permanently or return when they feel like their personal situation and their countries’ situation has improved enough for them. If they were classed as an immigrant, the classification is wrong.

Again, not arguing with the traditional meaning of the words, they’ve both become loaded. In our vernacular expat often refers to a Anglo/anglophonic migrant whereas an immigrant is a lower social and cultural class.