Wasted 150 runic splinters, How should I spend 850 div to upgrade?

You're missing so so so much damage on your bow, amulet, quiver, then rings in that order.

Not familiar with the build but how quickly did you kill the 100 runic splinters version? Damage looks low, bow should be upgraded, your boots need more ES and/or life, your amulet is not good enough, headhunter doesn't help you during that boss fight, your rings are purely offensive.

You need to get deflection rating on your boots, huge defensive layer you're missing that fubguns pathfinder has.

You want to have t1 Deflection on boots to reach roughly 50% deflection chance. This is on top of your ev for some more survival. Ideally daggerfoot boots if you can afford it. Doesn't take that much currency, craft is under 100d I think.

Amulet is a huge source of defenses. Look for max ES, max EV, global defences mods. Don't sacrifice +skills tho.

https://poe.ninja/poe2/profile/S_P_A_R_T_A_N-13-7925/character/MiniGoop

Im running the same fubgun build OP. Far from perfect and I still need some upgrades myself but going well atm. Occasionally get 1 shotted by bosses so need to fix that and deflection on boots is my next upgrade.

I changed his atlas tree in a few places for more energy shield, still not 100% on that.

If anybody else sees anything I need to change or upgrade, it would be appreciated.

I am no expert , but Maybe a Little of défense on 1 or 2 of jewels Will help , corrupt your gems and switch a couple of things in your tree … but like I said I am no expert l needed help from somebody of the group to reach poteintial on my build and I need to keep working on it. One other thing I believe should help : add some deflection ( because you have a full évasion build ) correct me group if I am wrong

23k ehp is honestly not bad for a pf, damage looks to be severely lacking. First upgrade should be a bow imo. Pfs best defense is killing off screen.

Is Hyrrie Ire worth it for this type of build? I understand the benefit of double evasion when not hit recently but for me felt lacking when you could a nice ES with a well rolled Sleek Jacket.

For OP, your ninja does not show any anointment in your amulet. You can get nice extra damage there. If you buy a new one be sure it is not corrupted or sanctified and of it is, be sure it was already anointed with something useful for your build.