Iron golem is a cool concept, but I always end up not using him outside of early game, because abyss knights and hawks scale much better with base points (they get increased minion count in addition to soft point bonuses).
Giving him some kind of hard point scaling seems like an appropriate fix, this way it is still a choice which of the summons to invest in (If we put some points in defensive skills, which we have to in order to survive in higher content, we can only really max 2 summons beside veil king.)
The simplest hard point scaling would be to give an additional iron golem at 20 hard points. But that makes it an all or nothing choice. I think it might be more fun to give his attack proc missiles a chance to pierce enemies per hard point, capping at 100% at max level. This should make his clear speed good enough to matter later on. Making iron golem focused on clear instead of single target also fits with his 0% resistance feature, which makes him pretty bad at surviving in boss fights.
I am talking about pierce as in vanilla d2 missile pierce, not resistance pierce. I think that used to be a stat on some items and was mostly only relevant on amazons for multishot and lightning fury.
Other than that, his usefullness is also hindered by being melee, running towards enemies and getting stuck. This problem gets "averaged out" in the other summons by having a higher minion count. For the single golem, this problem might be mitigated like it was done with veil king: Make him non-colliding with obstacles and give him better movement and attack speed.
Thanks for giving us the opportunity to give feedback on this awesome mod,
Best Regards
Some guy