I gave the Headhunter a few more tries. I was rather disappointed. My ranger kept getting killed as it has been. While I could gain some modifies they never felt like anything that great. Granted I was running tier 1 maps.

Don't be dissapointed tho, headhunter was never an item that makes your character strong by itself.
I think you still have a lot of things to improve. Leveling up itself will give u lots of damage from gem levels and a lot of HP( 1.800 hp I guess some monsters from Act5 could kill you haha:D) then as u say u have to get Ventor Gamble's which will cap ur resistances and of course helmet. I guess u probably don't have all the LAB's done, which will be a HUGE thing.

Besides gear,levels and labs, HH its a lot about monster density, the best buffs are granted by Beyond monsters, so once u buy this mod in map device u gonna see a huge difference but then u need a lot of regular monsters to spawn more beyonds, so using sextants on watchstones, scarabs especially Elder scarab, Legion Scarab, Harbringer Scarab/Abyss/Breach, and then if u running Tower map for cards then Divination Scarab. U might also invest into watchstones with chance to spawn another beyond monster. HH playstyle is all about juicing the maps. I love it but the worst part of playing with HH is that u need to spend a lot of time on buying scarabs, sextants and all this shit. Overall, without keeping the good density, you will lose buffs before you regain new ones.

I think you should also consider helmet called Asenath’s Chant and then put those gems in it Sniper’s Mark - Tornado - Hydrosphere - Onslaught. They will trigger every 0.5 sec everytime u attack. So basically u getting so many things. And then you have open slot for a better flask instead of Onslaught one. U can get Dying Sun for +2 projectiles for example, combined with +2 projectiles from Ascendancy its POG.

And to be honest with all this MF gear the only way to pump your damage besides those things I mentioned is either Cluster Jewels or lots Abyssal Jewels.

There is my video when I played with HH, I started ramping up from 0:30, then I constantly been able to keep up the HH buffs at around 30+ which u can see in left corner.

Have fun with finishing the character! I hope I could help with some of the tips.