It's not the end of the world - never said it was. But by your own math (6-8 hours per reward track), having done the reward tracks for each dungeon at least once, that's 48-64 hours I already have in...and I've done some of them multiple times. So having already spent the time and "done the thing", seems like I should be able to spend the currency I already earned.
If I have to do 40 dungeon runs...well I can do that. But that still doesn't mean this was a good change.