Beginner player caster (Warlock) need advice about Spell Hit chance, 13 SP = 1 Spell Hit chance ?

Hello, I am a beginner player, I need your advice, I learned that 13 Spell power = 1 Spell Hit chance, is it true? As a Warlock player, I'm interested, why put a cap of 16 Spell Hit chance on our equipment then? We could just put the spell power on our equipment, couldn't we?