Well, at the time there was (Chinese?) detection of some seismic event close to the “turning” point. That was dismissed. As for the open ocean, that is thousands of mi away from land and possibly many miles to any craft that would have any such capability or desire to use it. One also does not know just how much impact the craft actually would have - it could be slow and make a rather nice acute angle into the water, with less catastrophic impact than a headlong rush or somersault into it. That changes momentum and impact. (And bear in mind that aircraft are built to be light as possible.)
What happened with Air France? It was in the open Atlantic. Don’t recall if anyone talked about getting signals about shock or any such. And the Atlantic is narrower and probably more traveled by ships and US subs, especially where it was.
While the Air France planes remains were difficult to locate and retrieve, I don’t think there was any doubt about it having entered the water. Perhaps some of FR’s nautical and audio experts could chime in here..