I fly 80k - to 100k per year on Alaska and the only time I have had seat back entertainment was in the old Virgin America jets, and I don't think that Alaska plans to add them as they have an app that allows you to watch movies and other shows for free with the app. For the record I prefer being able to use the app with my laptop, tablet or phone over a seat back screen.

I would guess that there are lot more issues with AA to SXM over the other airlines, they have a lot more flights. I have had very few issues with AA, their jets are not that far off of any of the other airlines. They all seem to fly their Richard Nixon signature edition jets to SXM and other Caribbean spots.
Cheers!