This gradual thing makes more sense to me.
But looking at enlightenment like its a light switch, where your not enlightened and then all of a sudden you are enlightened, is concept I cant relate too.
We can have truly sudden and unexpected insight that can transform us/ However mostly the sudden enlightenment is for a handful of people throughout time (the real sudden enlightenment).
But when people would speak, it would sound like their talking like its a light switch.
Some, more Zen than not but not just. But the reality is gradual and even transitory (people's behaviour and insight is unstable up to a point). In fact technically even Nobel Bodhisattvas on the Stages who have directly seen emptiness have a degree of instability since on the lower Stages they have to progress within x numbers of lifetimes or they regress to some extent (so on the 1st stage they are supposed to have a limit of 100 lifetimes or else their insight degrades although this is a little controversial).
In other systems "sudden" enlightenment means over a lifetime or at death.
So sudden is really gradual except possibly for a small handful of people.
_________________Kirt's Tibetan Translation Notes
"Only you can make your mind beautiful."
HH Chetsang Rinpoche