Might wanna read the wiki entry on Grey Jedi.
Onscreen both Luke and Rey used dark side type powers (force choke/lightning).
That doesn't mean that they were "neutral", which is essentially what "Grey Jedi" are supposed to be.
Luke and Rey, on screen, are both still of the Light Side. They may use a power once or twice, but don't fall outright. In current canon, there's Dark, and there's Light. Nobody lingers in between. The Force is a step function, and there is no saddle point to rest in the middle.
I can understand the pushback on Grey Jedi. They are, in effect, trying to have their cake and eat it too - all the powers, but none of the drawbacks.