Honestly, I've been using Determination since HW and apparently Determination did see an increase to how effectively it affects things with the expansion.
In HW, when testing between myself and a WHM friend, in Diurnal stance, when she had about 70 more MND than I did, but I had a couple hundred more DET, my healing (Benefic vs. Cure and Benefic II vs CureII is what we tested with) was actually a bit higher... but we also noticed that the gap between the lowest heal and the highest heal seemed to be larger, too. Whether or not that was working as intended, we don't know. And we haven't looked into that since the expansion either (and it would be hard to make direct comparisons now, to be honest).

Crit would probably have the most meaningful impact on this expansion, considering the way they implemented crits into various kits this time around, but I'm still going to go DET just because I've been doing that the whole time and it doesn't really feel like it makes the biggest difference one way or another.