I still wonder if it's possible that your perspective from the boat affected what you saw versus what happened. Two independent sensors corroborate that the AC started spinning wildly during the last 2 seconds of flight and indicate that it lost about 45 feet of altitude (basically straight down) during those 2 seconds. From your vantage point, that could have looked like it drove itself straight into that rock but I think it unlikely that both the baro and the Z axis sensors (which I believe are independent) say it dropped 45 feet in 2 seconds right at the end of the log. I know I've been confused more than once into thinking it's taking a straight line when it is really falling, particularly when it is moving basically in a straight line away from you. If the map is accurate to the level we think it is, that still points to a possible hardware failure in my eyes. If it started spinning wildly and dropped from the sky in open air, the only thing I can think of is an Esc failure (based on the stick input, it doesn't look like CSC is involved). Which I think you could pose as an argument to DJI. Given the data, I can come up with no explanation other than a bird strike or a hardware failure that would cause what I'm seeing in the log and on the map. If that were my bird, I'd have to argue to DJI that (regardless of what you saw) the log indicates that it spun out of control while at about 54 feet altitude, and dropped out of the sky. That's not just a "buttered up" excuse. That's what I see in the log.
Keep in mind that I'm not one of the log-pros on this forum. I'm just going by the CSV log file. Maybe someone who has access to the full log can look at motor speeds and other parameters to corroborate (or contradict) what I'm seeing. I'm pretty new to log diagnosis so maybe I'm all wet but to me it looks like the thing had a hardware failure near that shoreline.
Mike