We were on the same cruise and I think most of the stress is caused by US Govt requirements. Yes it was a little stressful ensuring we were negative before the cruise (and because we left Australia early, we had to find somewhere in Southampton to do the test if we wanted to avoid the test at the pier) but it was strange to see Brits and Aussies without a care when it came to returning or flying home. We don't need a test to fly home and we flew back last night after 9 days in London after the cruise. In London you wouldn't have known that the virus exists and we didn't need to worry about returning home positive or negative. It was obvious that some people on the cruise, particularly towards the end, were not wanting to risk it, and understandably so if quarantining was a possibility.
Unfortunately most stress is now down to your Government regulations which seem to be out of step with the way the world is going.