and those are? Your description does not really fit with a stuck valve, but who knows.
Do you have an engine monitor, data?
History, has this been a new occurrence or has it happened before?
From your text the shaking happens WOT, and then diminishes when the throttle is reduced, correct?
What lead you to look for a stuck valve in this cylinder in the first place?
Those are honest questions trying to analyze what's happening in your engine. Not sure about picture #2, is that the guide with the borescope going thru? The valve itself looks ok, no seizure marks on the stem, and the seat face and margin look ok considering the engine hours.
Regarding the observed taper on the guide, the proof of abnormality would be given by performing the wobble test, as this measures not only minimum but also maximum lateral play. Yes, I guess comparing it "manually" to one of the other cylinder would be a step in the right direction.