Our definitions of Priority levels are mostly a chain of "lower than the previous higher value". Which isn't too great.
I'd call the current definition of "low" unrealistic: "Less priority than Normal, but someone is still planning to work on it." IMO that's often not really the case because resources are only in FOSS theory unlimited, but not in practice.
"Lowest" sounds belittling and demotivating, so I'm sure that many people do not set it, also to avoid follow-up discussions with disappointed task authors etc.
In reality, I do not see a real difference between "Low" and "Lowest" so I propose to merge them into "Low", and give "Low" the current definition of "Lowest": "Nobody plans to work on this task, but we would be happy if someone does." Because if we were not happy that someone works on a task it means that we do not want to see the task resolved, and that means the task should have "declined" status.