Are there airline crashes at sea where there were no large human remains? Or does the lack of large body parts not indicate anything definitive?
Yes, to both questions.
I was aboard the first specialist responder work vessel which attended the wreckage of the Itavia DC9 in 1980. We had been working in the straights of Messina and as we had two manned submersibles and a crew of hydrographers we were immediately despatched by the Italian Admiralty to investigate the scene. Our gear was limited to 600m and the depth at the locus was much greater than that, so our onscene work was limited to surface recovery only.
At the time, there was no doubt in the minds of the two senior officers who we had on board from the charterer that the aircraft had been shot down accidentally by the usual suspect, mistaking it for a known Libyan MiG intruder. Subsequent investigation of the seabed wreckage cast some reasonable doubt on that and it's a bit of an open verdict as to how the aircraft was brought down.
One's first impression on arrival at the scene was the incredible number of bits of paper were among the more solid flotsam. Thousands of pieces of paper. Of the human remains, there were a hundred or so that we recovered and the local fishing boats who arrived a few hours before we did recovered many more, but mostly very small. The largest were recognisable parts of limbs, but most were really quite small.
From other work on the seabed in other cases, I've found quite intact remains of almost whole bodies within and very close to airframe parts.
When an aircraft comes apart at very high speed and high altitude, eg the shootdown of an Iranian Airbus by the usual suspect, ejected occupants tend to be stripped of clothing by the airstream during the deceleration to terminal velocity.
From personal experience in several such field investigations I expect that the condition of size of the remains on the seabed will be quite different to those found on the initial surface search.
I doubt that the lack of large body parts indicates anything definitive. I also doubt that a bomb is indictated by the skimpy evidence we have so far, but we need more data before we can analyse the three principal postulates.