Au contraire. The more ways there are to drill down to a particular sailing, the easier it is for people to find it:
- If somebody only knows the name of the ship, then they can look for ships with that name. If that's all the information they have, then we have already provided a way for people to drill down that way.
- As you say, for many sailings, it's a lot easier to find the date of arrival than the date of departure, so probably lots of people will want to drill down that way.
- But I have worked on several sailings where I knew the date of departure, but not the date of arrival. If that has happened to me, then it's bound to have happened to other people, so I don't see any point in depriving those people of the ability to drill down to find the sailing on the basis of the information they have. (Especially when it's the only information they have.)
We already have parallel ways to drill down to find ships (by name, country, company, or year of launch), and, for that matter, there are multiple ways to drill down within the occupations categories. It doesn't have to be "this way" or "that way". It can be "this way" and "that way". That way, the system benefits the maximum number of people.
Remember that there is no limit on the number of categories. We don't have to delete one category before we can add another.
Looking at the wider picture, I'm afraid that I have a hard time with any project saying, "Yes, we know that everybody else on WikiTree is doing things this way, but for our profiles, you have to do it that way." It just doesn't strike me as being in the spirit of collaboration. Nor helpful to newcomers, for that matter. WikiTree has a steep enough learning curve as it is. Expecting people to remember exceptions to general rules would just aggravate that problem.
And, as a footnote, I have to say that, for those sailings to Australia or New Zealand (or North America, for that matter) that I have worked on, I put in a lot of time finding departure dates (at least in some cases), and I would be exceedingly annoyed to have all that work thrown out just because somebody doesn't see any value in that particular bit of information.