I’m glad the guide has been able to give you insight into how I build my characters! The build presented is very limited in terms of gear, but also components, since I wanted to make sure there are no required blueprints for it which cannot be bought from factions. Using stronger components in armor / jewelry can strengthen the build as well as whatever appropriate legendary or epic gear you find. Generally speaking, I want my main skills to be maxed out or as close to maxed out as possible. So if you find gear that lets you spend fewer points in Shadow Strike but still have it at 26/16, it can free up points to go elsewhere.
To improve this build for the endgame, focusing on Shadow Strike is still a viable way to play. If you can get your hands on the Korvan Dunefiend set, it directly supports the same play-style as the leveling build. Fordprefect’s Dunefiend Witch Hunter build makes good use of it, though the amulet might have to be changed since a patch made it so that particular prefix messes with Shadow Strike damage conversion.
One of the things I love about Grim Dawn is that respec’ing is fairly cheap, so you can experiment with changes to your characters and it won’t cost you too much, even if you want to change them back. If you want to try creating your own builds, look at what other builds do in terms of offense and defense, see which aspects you enjoy or which items you think are interesting, and give it a try based on the items you have! You don’t need to copy builds 100% for them to be effective.
If you want to go in a different direction, the Vileblade Pact set offers Amarata’s Blade Burst focused builds or you can try a build like RektbyProtoss’s Balegor Witch Hunter. There’s also a chaos Rah’Zin’s Witch Hunter if you want to dual wield a different type of damage. Though this Demonslayer Witch Hunter post is old, it should still work if you want to focus on Phantasmal Blades and Blade Spirits. Lots of different options out there to explore!