That's the problem though. People look at EN as a metric to compare against, but that's just wrong. Tuning of EN was wrong, tuning of other instances
shouldn't be the same.
I made a picture to illustrate it more easily:
Helya is
not harder than Lei Shen, Garrosh, Blackhand or Archimonde on the same difficulty. Yes, she is massively harder compared to Xavius, but that's only because Xavius was a joke.
It's not ToV difficulty that's an outlier, the EN difficulty was.
Now that being said, there are two points to be made:
1. Flex scaling wasn't implemented very well, particularly for Odyn, which is way more manageable with larger groups (you have 5 players fixated, which in a small group can be pretty much your entire raid, while you still have 20 other "free" players in a large group to help out). This could be adjusted by lowering the health of the mobs more or just decreasing the number that spawns.
2. The instance is very short, making it difficult to "farm the first easy half to gear up for the later harder bosses". It
only has the later harder bosses.
What you
can do is farm some gear in +1 difficulty of EN. I know it sounds weird for normal mode players to be required to farm some heroic and for heroic players to farm mythic, but the difficulty of the instance is so low, that it is possible. At least the first 4 bosses of EN can be killed because their difficulty is really about 1 more difficulty lower than where it should be.