Brioche bread texture
I am pretty certain you simply overbaked your brioche. "Bland and dry" is a very common symptom of that. Also, if we look at the recipe, you had a quite small loaf, which you baked for 40 minutes. 

The first solution I'd try in your place is to bake to internal temperature of 96C, then remove immediately from the oven and swaddle in a kitchen towel, possibly spraying with water before covering. 

The other things you can do are finer tweaks, but they shouldn't have that much of an effect on the dryness as such. You have way too much yeast, especially for an overnight raise. I've read books that suggest using more yeast for a brioche, but that's because they also have a shortened raise and/or baking from cold (to keep the very buttery dough firm when forming). I personally don't care much for long rests, so I would maybe reduce the yeast only partially (maybe using 2.5 to 3 g) and do two raises at room temperature, as with normal white bread. If you want to keep the retardation, then use less yeast, about 1.25 g. But since your dough is neither under- nor overproofed, the amount of yeast shouldn't have much impact on texture, mostly on aroma only.