There are no problems with my statement. I already prefaced with saying I have no idea why they are using it in their design...like I literally don't even understand why they are doing it...but the idea of what adding an additional dmg to resist in the game is just numbers. Your point number 2 already proves that you understand this, but I don't think you realize it.
Number of gear slots are finite. Number of gear acceptable with all resist are finite. To achieve peak damage efficiency and resist, you would now have a lower overall total of each resist b/c you will use at minimum one slot for a new resist. You see what I mean?
Again, I have no idea why they are saying this is a part of their class design b/c that bit makes no sense to me.