Hey guys!
General response to the topic at hand.
I think the problem with the Hill Giant's damage is simple. Its a typo. I am convinced it should be dealing 2d10+5.
The Hill Giant is being 'out muscled' (if you'll forgive) by pretty much every monster of a roughly similar level (whether Lurker, Skirmisher, Soldier or whatever). Brutes should not be dealing less damage than monsters of different roles of the same (or roughly similar) level. It simply doesn't make any sense dealing 1d10+5.
I have boiled the damages of all the monsters down to a bare minimum and it looks to me as though the following is the standard design parameter (give or take a point). I had initially supposed that Brutes were dealing double damage off a Base 4.5, but further study shows that probably isn't the case.
Brutes: Base 9 + 1/2 level average damage
Soldiers: Base 8 + 1/2 level
Artillery: Base 7 + 1/2 level
Lurker: Base 6 + 1/2 level
Skirmisher: Base 5 + 1/2 level
Controller: Base 4 + 1/2 level
To pick up on a few other points:
The Hill Giant is not wielding a human sized greatclub in one hand. Its obviously wielding a giant sized greatclub. Theres no reason why it would be wielding a human sized greatclub, giants never have in the past, the illustration shows both Hill Giants with two hands on their greatclubs. Giants use two-handed weapons...thats what they do!
The Earth Titan, using its natural weaponry would therefore deal slightly more damage with a single punch than the Hill Giant would using a Large Greatclub.