The only thing I use Humanity for is Kindling bonfires, I never summon anyone and I am doing fine for the most part. Really feels like Insight is the better version of the mechanic.
For real, the only thing I have gotten out of staying human for any length of time are some people with weapons from farther into the game invading me, but I just chuck fireballs at them and killed them. Then they dropped a weapon I couldn't use because I am a Dex build and they just used ST weapons. I mostly just kindle the bonfires with humanity. Haven't summoned anyone even once.