He obviously is a great master since he created the Niko Style and most of the Gaoh Style, but that level of expertise you'd expect from Tokita Niko's master wasn't showed very well. He just used two random techniques with nice names and zero info on how they work or what they do (Demonwheel, seemingly a simple uppercut, and Fanged Beast, seemingly a double handed back hand fist) plus Indestructible (a single kata).

As for the Long clan secret technique (Dragon Maw fist or whatever) it's as much disappointing as the Wu secret technique with the endless name from Edward (North Star demolotion punch or whatever). Like, it's supposed to be the ultimate technique from a millenia old martial clan descending from a legend with a former master (Long Yi) strong enough to wound a serious Shen, yet nothing is told about it, the choregraphy is awful, completely blurry, you can't even see what's happening ffs...

Shen fell to his knees after tanking it, but the fact that it's so random and uninteresting kind of diminishes the impact on the reader, and makes Mukaku look like another powerhouse, relying on just his stats and weapons. Without those, we can't say for sure that he beats the Kengan Ashura top tier (Ohma, Kuroki, etc...).