Hey thanks for the long reply :) must've been a while for you to type that.

Well my point in the Grey worm affair is that it really wasn't tied up as well as it should, from episode 3 to episode 7, they left too much for the imagination, we're all left with "could've" and "might have". It just fast forwards to, hey they're there when they're supposedly starving to death defending Casterly rock. I'd also like to know the source of the fraction of the Lannister army staying to keep them boxed in as i might have missed on that. The Unsullied were considered long gone by Dany, as she mentions quite alot she has already lost the unsullied and her two possible allies in Dorne and High Garden.

High garden scene was really shown as a surprise attack from a viewer's standpoint as it was symbolically parallel to the Euron ambush. The scene was also shown as something Jaime supposedly learned from experience from fighting Robb Stark.

The Lannister army didn't have siege weapons, and it's no easy feat besieging a fortification as seen in the siege of Riverrun, so it's safe to assume High garden wasn't much of a Castle but it should've been according to the books. With that said, if not for ego, pride or just plainly giving up, it was a bad move defending that place nor ask for reinforcements If they did indeed saw them coming, no ravens for Dragonstone? How long was the place standing? a few hours? it lasted for a few seconds in the episode, that my friend is rushed.

Still doesnt' explain how Euron fast traveled from King's landing then into intercepting Yara and how he got those ships in the first place.