I don't know what the point of this change was. It happened I think at the same time deserts became wilderness, so maybe the idea was to give a little something to mariner rangers? I think it actually hurts mariners as well as water forms more than it helps them though. It makes water areas really undesirable for druids, non-mariner rangers, and Outlanders, which means water themed characters will have many fewer possible fights in their terrain. It also makes the water commune that druids have kind of pointless. And it creates a really annoying situation for water major Outlanders, since they have to spend lots of time out of their niche just to get enough wilderness time to be inducted.

If it's important to give mariners terrain something unique, it's enough to just limit pathfinding and wilderness familiarity in water rooms. If they stay wilderness other than that, it seems like it preserves whatever the original change was supposed to achieve without the downsides.