Bguy7
The Dragon Lord
TBH it was somewhat on the glass canony side, though what some people like to believe that Darkrai was so much of a glass canon that Hercross and Gible weakened it severely enough which allowed Sceptile to land the final blow to defeat it and finish the job, even after it used Dream Eater twice, not once, it pretty much ridiculous and does not make any sense. It was majority of Sceptile's work with some amount of help from Heracross and Gible(that too majorly being recovered by Dream Eater).
And different Pokemon have different strengths and weaknessess. Darkrai being on the glass canony side does not make it any less powerful. It's just Darkrai's strength lies in its sheer raw power of Dark Pulse/Ice Beam, and it deadly status combo of Dark Void/Dream Eater, whilst its weakness lies on the tanky side.
I guess it more comes down to how you define glass cannon. When I hear that term, it makes me think of something that has trouble surviving at all, despite its damage output. Darkrai certainly didn't have an issue surviving battles, even if its not a tank.