Yes he brought it to the ground which was the right solution.
I think standing ngannou was in danger. Well both probably

does ngannous total inability to compete in the ring demonstrate that the standard in MMA is much lower than in boxing?

Well a MMA fighter who is very strong with his fits will never be a match for a elite boxer in English boxing , it's totaly different.
Ngannou has the power with his fists but no more , he doesn't have the technique.