Rare but there

The night missions have the other CE as a drop

It's rare, but it's still not 0%, so it's possible. In fact, some of events shop only give you 4 copies of Craft Essence, so you have to farm to get the 5th copy in order to Max Limit Broken it.

RNG for a ce drop are complete random

Some people can play for the whole event and grind with gapples

And not get 1

While some can get it day 1 with barely any grind

That's RNG for you, or maybe even life in general.

Does anyone know the actual drop chance for event CE?

Below 1% that's all I can say

Gamepress estimates between 1-2.6% for event CE drops typically. Evidently this data is sourced from Atlas.

Every event has a chance to drop the featured CE on drop quests.

I don't know if that's a personnal thing, but I'd also like to add that reruns tend to have a better droprate for CEs?

Like I usually get 1 or 2 CE drops on reruns, but it's way rarer on original events

I think I red somewhere that droprates on reruns are 2% instead of 1%, but I don't want to distribute false information so unless it's confirmed, do not believe what I just wrote. It's just my personnal opinion based on what I've experienced so far with events and reruns.