Honestly, if the right side of the Shadow tree was rebuilt as the dotless style, with Idol of N’zoth being changed into the Clarity of Power mechanics, it would fix 99% of the clunk. I believe that the two Shadow identities present in WoD were some of the best time I had playing Shadow in 17 years of WoW. Blizzard should simply steer the tree towards
Left Side: Classic Shadow (WoD’s Auspicious Spirits + Shadowfiend)
Center: Legion Shadow (reliance on Dark Ascension or Void Eruption burst windows)
Right Side: Clarity of Power Shadow (dotless gameplay built around Mind Spike + Mind Flay: Insanity for Shadow Weaving phase)
There. I fixed Shadow, made almost every choice relevant, and gave it three radically different gameplays.