I think your partially right but I also think some of it is a result of problems with the book series.
They needed to do something at Winterfell, they needed a "big" character death and they needed to get rid of LF 'cos he plays no role in the end game.
The way they went about it was terrible. I imagine the reasons were irony, his plans coming undone as a direct result of a "cunning plot". The Sansa/Arya/Bran relationship should have been the focus and they should have fit LF's down fall in this. Instead they did it the other way round, Sansa et al had to act in that way for LFs story. It's shitty writing pure and simple.
How about something like this instead -
1- Stark kids reunion
2- Mistrust between all three but not outright hostility. After everything they have been through and the fact they weren't exactly bessie buds prior some mistrust would be expected.
3- LF starts his plan, Bran immediately grasses him up to Arya. She stabs the shit out of him.
4-The rest of the season can then be dedicated to the fallout of this. Will Sansa think that Arya cunningly disposed of her smartest ally? Will Bran mistrust Arya seeing how violently she reacted to the information? Will Sansa think Arya/Bran are coluding against her? What of the Vale Lords? etc etc. So much potential. Plus how shocking would that be? LF brutally murdered early on in the series?
I wont mention the acting (although obvs I have) but I do think it plays a role.
I don't understand what they are doing with her at all. That whole Dickon/Randyl thing baffled me. What was the problem? Tyrion made zero sense. Loads of the soldiers didn't kneel, where they to jail them all? Quite honestly that seems like a good deal in a war. Be on the losing side, refuse to kneel, sit out the rest of the war in a nice cell with food and water. Tarly had betrayed Olenna who died as a result. Plus Tyrions reasoning was "Wont somebody think of the Old Houses!?"... but if you are so hawt for the old ways then surely they should die for betraying their liege lady.
Anyway the point is the show wants us to think this was bad. Then... totally forgot about it. I mean the "Game of Thrones" doesn't have that much life left in it. Can Dany go totes Mad Queen in 6 episodes? Whose she gonna go Mad Queen on? The army of the dead?
Part of me thinks they just did it to fuck with book readers who are convinced shes batshit.
I agree with you here, the showrunners wanted the main characters to get together and have all those reunions and I don't think they will get another chance.
I actually give this one a pass. I think they are patching up book stuff that simply can't be explained in the context of the show. My guess is that he is called Aegon in the books and he was legitimate somehow and both those things make total sense but have complex reasoning behind them that requires background (or page time) we don't have in the show.
Here is an interesting question though. How come he is the legitimate heir to the Iron Throne? I can't remember if it was Sam or Bran who said this but either way it doesn't matter. So let's accept whichever one said it was privvy to Jons letter saying he had bent the knee and accepted this. It doesn't matter, Dany is attempting to be a ruler by conquest, the legitimate heir is probably some Baratheon 3rd cousin. Even if they accept Dans rule then as I said she rules because she conquered. Her reasoning may be cos her Dad was king but the actual reasons are Dragons, Dothraki and Unsullied.