Brace, no need to get nasty. The legal position is that accountability (responsibility) cannot be shared, fact. All the manufacturers manuals share this view. If on one of your Line Flying UnderSupervision flights your second in command disagrees with you on whether to ditch in the North Atlantic, depressurise at 25,000’ etc who makes the final decision on your flaming aircraft. I made it clear that if he had been released, signed for the tech log and I was in the RHS that was his call. A few airlines allow non PIC reject decisions (EasyJet tried it and reversed it in short order). In this case you would have something to respond with. If you want to see the startle effect operate AP disconnect in the sim at V1 -10, most will stop. If a new LHS had a nose wheel disintegration, huge bang engine surge he rejects goes off the end and people die YOU will be held accountable by the lawyers (ask one, I did years ago).