I thought it was a good analysis question. It was a nice easy one because we were able to see the issue multiple times. The techniques that were used are valid so the issue isn't there. If the techniques are valid then then we have focus on the practitioner's skill and his ability to applied the techniques against what he was facing.It's a sacrifice kick. That's a technique. You fall down to help get you the height and power (similar to the effect of a trebuchet) and to get your head out of striking range.
It's more effective on a padded surface, especially if there's a break in the action when there's a fall. It'd be a bad idea in other situations.
This thread is the equivalent of saying someone's fist sucks when they're doing a spearhand, or that someone's kick sucks because they hit with a knee on a knee strike instead of hitting with the foot.
You've been on this forum long enough that this can't be due to your being a beginner. But this post reads like a beginner saw this kick and thought "I stand up when I kick, he falls down, what an idiot, I'm so much better than him."
He has good kicking ability but it's not suited for what he was facing. What I saw reminded me oh how beginners try to kick hard and the kick is what takes away their standing leg. This often happens to beginners when the kick higher than what their root can support so the weight of the kicking leg moves the standing leg. It's the same concept of how people's punches throw them off balance. The only way to solve this issue is to use power and learn how to root that standing leg.
Most people don't have this issue at this level because they learn rooting through punching and that concept translates into kicking. It doesn't take long to fix, but it's not something I would want to try to fix in a competition since the first instinct would be to kick lighter and not harder.