It is correct, 14 palisade*xml files indeed, four of them inherit template_structure_defense_wall_gate, so they indeed have to replace the SpawnEntityOnDeath.
The rest of them can just inherit the entry of template_structure_defense_wall.xml, even though no template_structure_defense_wall_foo.xml uses that entry.
An alternative would be to remove it from the parent and add it to every child, but that doesn't make a significant difference.

The size 2x2 is definitely too much and very apparent ingame, but it's still better than using foundations.

As with D643, we should delete the now unused and still unusable files in the same patch that made them unused.

Thanks for the patch! Those foundations have been annoying me since I saw destroyed foundations the first time! (Didn't even notice it for other buildings).
Also thanks for fixing the other item on Danubius :-)