For what it is worth, Scott Brady (Expedition Overland) discussed in one of his podcasts removing a Grenadier with a dead battery from a shipping container. He confirmed (as noted earlier in this thread) you can move the transfer case shifter between H and L positions to achieve a neutral condition and rolled it out of the container.
So how deep was it? It certainly doesn't look that deep. I was never a fan of the side intake, can only say it is really disappointing to hear that is all it took to take down your Grenadier. IMO, it should take water over the hood level to stop these trucks (particularly diesels). If that is all it takes to get water into the intake, it is a poor design at best.
I would think engineers could design it (particularly with a side intake) so there is a rather deep draining 'reservoir' that would have to fill before air taken from the top could make it to the engine intake. Add a floating 'door' to close off the intake and stall the engine, but not allow it to ingest water.
Really disappointing to hear, and sorry you have to go through this..
Rather Infamous area that floods, this one was at three ft or so..
Many Land Rovers make it through without issue..