A literal interpretation of Övberg's testimony cannot be reconciled with a collision with a 5,000-tonne submarine according to physical law. I don't have to apply a value judgment either to the witness or to the testimony in order to note that the evidence cannot be explained by a proffered hypothesis.
The credibility of a witness is measured solely in the degree to which their report coincides with what actually happened, and with objectively obtained evidence. Their courage or bravery has nothing to do with it. I can look critically at their testimony and attempt to reconcile it with what can be known by other means without having to comment on their character.
You, in contrast, seem to want certain eyewitness testimony to be taken as literally and incontrovertibly true, including all the attendant interpretation and inference, and that anything other than that is an attack on the character of the witness. That is simply not how a credible forensic investigation occurs.
I dismiss the literal interpretation of the witness you cite as evidence of the submarine collision you've hypothesized to explain it by the simple fact that it's physically impossible. I have no problem believing that the witness exaggerated his perception of whether the ship actually ceased forward motion. I have no problem with the witness simply having been jolted off his feet by the unexpected motion of the ship. These are not disrespectful interpretations, in light of other evidence. This does not call his character or fitness into question.
As to the science, you've made it plain you have no use for science that doesn't confirm your beliefs, and you have no problem defaming the experts who disagree with you. It's therefore rather disingenuous that you're trying to trump up an emotional argument for why we should consider eyewitness claims paramount.