While this can’t answer the question individually on whether you should go wide or go KDP Select, it’ll give you the best picture of what the market is doing. That way you can make an informed decision.
Also, a lot of people missed the last “not-a-report” report they put up, with the slides from the Digital Book World 2017 conference. If you haven’t seen that yet, you’ll want to: it’s pretty eye-opening on how much of the print sales have moved online.
That one has some pretty fascinating numbers, including breakdowns that show some smaller genres lumped in the large “trad pub is still dominating” are actually far and away fast-growth for indies.