Less duplication by specifying the status bar in template_unit_ship.xml rather than in its children.
You're correct, currently the generic fishing boat template does not specify a status bar, which means it defaults to the values of the template_unit.xml file. If desired, I suppose I could insert those into the fishing boat to preserve its status bar size.
However, is it really important that the fishing boat has a status bar different from all other ships? Does it convey some information to the player that will be lost if it's standardized?
For comparison, without this patch:
and with implementing this patch:
I guess the barsize is related to the size of the visual actor, and the big one might or might not look uglier. (Perhaps it becomes more clear if there are more ships or more units in general, but probably it's not so bad)
Well that tells us that fishing ships are intended to have a regular sized status bar, not the larger one from bigger ships. I would say make a copy of template_unit's status bars for that template and keep your change otherwise.
Personally though I'm also fine with giving the fishing ships a large bar similar to other sips.