Funny that you mention him, as I was just thinking about his teachings the other day. It can be tough to really dive into preliminary practices because of the anti-idolatry cultural conditioning of the West, and I have certainly found myself thinking more about Vedanta and trying to answer this exact discrepancy you mentioned - are 'all of a sudden' mystic experiences that simply "click" as valid as ones that require longer periods of conditioning?

I think the answer lies in the notion of irreversibility so aptly captured in Mahayana. The "waking up" to a higher order of awareness seems to me analogous to Vipassana analysis, which is itself said to only be totally complete and deep enough to enact powerful change once it's combined with shamatha. Judging by Adyashanti's own history of practicing Zen for decades, I think the longer road is the more trustworthy for those committed to permanent awakening, and the contemplations of 'Who we are' can reverse the tide of delusion (until more powerful conditioning eventually takes over if triggered by the right circumstances).