It automatically cancels when they use their oni techniques. The others can't do it either. The gravity assaulted them both times the kings used their arms.
So they can't use enbu and demon cells at the same time. Got it. But they still used their demon arms and when they did Bambina just shrugged them off, so Toriko's demon arm should not be of any threat to Guiness and that whole scene of Guiness dodging the attack suggested the attack as a threat.
The chapter explains how Toriko has always been this powerful subconcsiously since awakening after his fight with Star. His resolve to capture GOD I suppose is similar to the resolve he had to rescue Komatsu which is why it's only just now manifesting in a combat situation.
Yes, we all knew he had that potential. It's just the timing for it to come out now is more convenient for the plot rather than sensible. Komatsu's life depended on Toriko grabbing Bambina's balls and yanking them off. His life literally hung in the balance between 2 worlds at that time. You'd think Toriko would unleash hell and unlock his true potential right then and there fighting one of the 8 Kings. In fact, in that same link you posted it was shown Toriko was ready to unlock that drive right vs. Midora to save Komatsu's life when it wasn't even in immediate danger so…what's the difference now?
Convenience. Toriko needs to stand up to the Wolf King, even if temporarily, and Shima already pulled the Oni out of a hat trick so now it's conveniently time to unlock his "true power" which will turn out to not really be his true power.