I agree this isn't wasn't the best season from a story telling, but I think you're reaching a bit as per plot holes.
- Grey Worm and the Unsullied were only trapped at Casterly Rock because Euron burnt down their fleet. While a fraction of the Lannister army stayed behind to keep them boxed in, while the main host attacked the Tyrells.
We all know what happened to that main host when they ran into the Dothraki and Drogon. With the main force defeated, the unsullied would have easily defeated the small army boxing them in. They could also have gotten reinforcement from the Dothraki who are all on horseback making them a very mobile army. No holes there.
- No issue with Euron's attack or Jaime's march on Highgarden. Euron could have easily had a spy within Yara's crew, he could have had scouts along the way to Dorne, nothing illogical about a surprise attack in warfare. The closest thing to a plot hole would be how unprepared Yara was for the attack. But you can easily chalk that up to Euron's prowress as a captain. He is the greatest captain on all the seas after all.
As for Highgarden, they saw the army coming, they just couldn't do anything about it. The Tarly's had bent the knee to Cersei and that gave the Lannister army the numbers. That was clearly conveyed with the scene with Lady Tyrell looking down on the Lannister army from her balcony with a defeated look on her face.
They knew they were coming. They did was any smart army would do. Play defense inside a stone castle and hope the fortifications make up for your lesser numbers rather than leave the safety of the castle and make things easy for the enemy.
K, I'll stop there. This is getting rather long.
Yeah, the whole "suicide squad" thing was stupid, no defending that. They didn't even take horses. I think we can all agree that the entire beyond the wall fiasco was the worst-written segment in the history of the show.
What kind of broke ass king roams around without a horse?
Dany should have been there earlier...
Her not having scouts to inform her, what is happening is just stupidity on the writers part..
It's something like over a thousand miles March and there's One road !!!!
the only reason the show had them completely take HighGarden is because of the Jeoffrey Confession...
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.