Yes, the upcoming collections don't have anything interesting for me, either, but then I have been collecting MAC for 10+ years, so there are many similar items that I own or I owned and sold them because they were not quite right. True about Angel Flame, but I think for example Jete would play the same role in a look, and as you hinted at, even if swatches vary a teeny bit, in the end being in a look it won't be such a noticeable difference that it is "necessary" to have both.
I am very aware that small differences can be significant when it is about the question whether a colour / tone is right for one's colouring or not, so it is possible that one shadow looks wrong and the other one perfect and they only differ by 5%, but when both are right for one's colouring / eye colour / overall look etc, then it´s just about the question whether one wants / wishes to buy another one or not.