Sadly, the fact of the matter is that 99% of players will never touch nightmare so "properly balancing" it is going to be way down on BW's list of priorities. When determining the game's general difficulty as well (not just on NM, but on normal), they have to tend towards the easy side or risk alienating casuals aka their money.
From what I'm hearing about 25-50% of people talk about doing a nightmare run, and if they don't they're complaining about hard being easy. Not exactly 1% of people complaining.
Personally I've found no healing of any sort is the way to make fights in general, and in particular boss fights challenging again. I fell about 5 times to Envy until I reloaded an earlier save just to do some min-maxing and respecing before that whole mission.
Anyway, no healing during fights, no tier 2 or 3 schematics, no overlevelling before any main storyline encounter. So far it's hellishly good.
There are other little tweaks too: no exp boosting perks (or maybe no reading instead), sell all research items, no dispel on fade rifts, no fade shield,