I was a level 42 champ when I completed this instance solo. I also happened to make a music video of it which I'll post the link below. Skip to timestamp 7:30 to jump to the boss fight. Also, (the following is copied from lotro-wiki) the boss has a knockback skill, which he will use on you, then run after you to continue fighting, which results in the fight moving farther and farther away from the starting location. If the fight moves too far from where it began, Taushakh will reset, running back to the start point, regaining ALL of his morale, and applying the skill Hardened Bark. Since Legolas is still in the area, Thaushakh will instantly re-aggro and the fight will start all over again, without giving Legolas and the player a chance to rest and heal up. Therefore, if knocked back, try to return to the location where the fight started.
You can see this in the video at timestamp 9:30. At the time I thought he was just returning to his meeting place with the Nazgul to instantly heal himself so after that happened, I positioned myself between him and the place where the Nazgul was trying to prevent him to run back there. However, by doing that, I think I was unintentionally compensating for that kickback to not throw me out of the area too far away from the starting location.
A couple of other things. Use Hope tokens. I wished I had them when I was fighting this instance. And try to use clobber and your horn to break his healing inductions.
Good luck!
https://www.youtube.com/watch?v=C9a-4bIgTL8