Hello there fellows!
I’m coming back to the game (2 years since i played last time), and necromancer is my favorite class.
I noticed that my skelletons and shoggot deals almost no damage (i’m lvl 343, using the Kedoran 315 equips). My other wizard (Pyro/Elementarist/Taoist) deal a ton of damage, almost oneshotting everything with the same equips.
Are the summons nerfed? or i’m playing wrong?
Thanks for your time :)!
Summons do low amounts of damage until you obtain a sufficient amount of SPR stat. Your SPR not only determines their damage, but it determines how much % of your stats (ATK, crit, etc) your summons inherit from you. If you don’t have enough SPR, they won’t inherit enough of your stats, and will do low damage.
In general, as a result, they only start doing more damage at higher levels once you can reliably obtain SPR on all your equipment items.
Thank you very much Crevox! 
If SPR determines the % of stat from my Wiz, then INT is also equally important to boost up my MATK for more dmg?
That’s right. INT increases your Magic Attack, which is then inherited by your summons into their PATK and MATK. Both INT & SPR are important and they scale off each other as a result.
You also need to remember to cast a buff for your summons to do damage (Desmodus for Sorcerer summons and Gather Corpse for Necromancer summons), and maintain that buff constantly.