It's an interesting argument. I know you, as I, can well recall the days of the long lines and mass groupings at the terminal with everyone trying to board at 11:00. At the time all check in was done at the counters where documents were checked, pictures taken, and room cards issued. The process often took (depending on port) 45 minutes or longer in our experience. At least it was that way with RCCL.
In some cases just before, but certainly resulting from covid, the check in times were initiated and early on rather strictly enforced. On line check in also came to prominence. And IMO the process smoothed out and was much shorter and more efficient. I know most people still hope for the earliest times (myself to some extent as well), but even the later times still have you on board reasonably early and, again in our experience, with far less hassle and time at the terminal. Not sure eliminating those slots wouldn't result in a return to the old days?
I wonder if with your Princess experience people weren't staggering their own arrivals or maybe staged naturally with flight arrivals, etc.?
Who knows, keeping everything else as is and with good staffing, maybe eliminating the check in queues wouldn't be a bad thing. I guess it certainly would be worth a try. If it didn't work out they could always go back to it.