Frankly the Necromancer Golem synergies are all messed up. Even without Golem Mastery Clay Golem has more life (because its life goes up each level), while Fire and Iron Golem has less and have a fixed amount of life regardless of level.
I have a thread where I suggest skill changes, and for the Necromancer section I suggested changing the way Golem synergies work:
Right now, you have Golem Mastery which gives life, attack rating, and run walk speed to each Golem. You also have synergies to each golem from the various other Golems. That is way too many synergies for Golem builds when you can only have one golem out at a time. It should be set up so that you only have 40 points into your Golem builds. 20 in the Golem of your choice, and 20 in Golem Mastery. That way you then have points left for other skills to support your golem. Of course, only the Clay Golem is currently balanced to work this way.
The easiest way to do this would be to move the current synergies: +20 Attack Rating (Clay), +5% Life (Blood), +35 Defense (Iron), and +6% Damage (Fire) to per each point Golem Mastery. Of course, that would buff the Clay Golem quite a bit. However, the only thing in there that really powers up the Clay Golem is the +5% Life (base damage for Clay is too small to be helped by damage increase). Thus, I recommend adding +20 Attack Rating (Clay), +35 Defense (Iron), and +6% Damage (Fire) to per point in Golem Mastery, while buffing the base Life for Iron and Fire Golem by +100%. (IE what you would get from 20 points in Blood Golem). Neither Iron nor Fire Golem will be broken by this (as they are both still less than what the Clay Golem is without that buff), heck I’d even consider increasing their base life by 150% to make them similar to the Clay Golem in total life. It would take a small step towards making the other Necromancer Golems viable. It would also help out the survivability (but not the damage) of the Iron Golem on items (Metalgrid, etc) as that has suddenly become relevant this patch.