So, what is Shen's theme?
Don't say ninja, because frankly no it fucking isn't. Shen has never acted as a ninja, popping from the shadows to assassinate people. He's always been a tank focused on protecting his team, as well as the quintessential "duelist" tank. His ult is a global "save my carry" button, and his E is great CC for peeling divers or assassins.
So, what did the rework add to follow through with this theme?
Well, his passive is just a better version of the shitty shield he had on his W, enabling him to take more damage so his team doesn't have to. His Q makes him a single target damage threat, chunking squishies and doing solid damage to tanks. It makes diving the carry a very risky prospect. Furthermore, it sets up his W, which is important. Shen's W is an amazing tool to protect your team and yourself from damage, creating a zone where auto attacks can't damage anyone. This is a super thematic ability.
All of these traits also make him a pretty strong duelist. His shield makes it hard to do lasting harm to him, his Q is a good steroid and has great synergy with Wit's End or Titanic Hydra, his W makes him immune to auto attacks (and auto attackers tend to be the best duelists), his E gives him more damage and CC to form them to take his damage as well as set up his empowered Q.
Shen's kit, functionally, is very thematic.
The problem is merely an aesthetic one. Shen's spirit sword looks, well, kind of goofy to a lot of people, and that's understandable.
But why sacrifice a great, healthy, and thematically on the point kit because of how it looks in-game? At best, he would just need an update to the visuals or something to make it look better.