Since it not that clear…
Summon scale with both Spr and Weapon Main M-Atk Stats (Not the gem or side bonus or int)
Their damage is quite good/viable compare to now if you check pretty much any necro post patch from Ktos.
Not sure the exact formula but, I think spr act as a multiplier (%) while Weapon M-Atk add a bonus base damage to summon.
If it the case, not going Spr for summon might result as a big lost compare to not going int for a nuker type mage. (Since you can have over 4k with weapon.