"The writers had no choice but to make stuff up and change the story because fire and blood is not a good story for adaptation" is a tired and lazy excuse for bad writing. (Salivating pandas response)
This argument seems to be the favorite of show defenders who don't think fire and blood is good for whatever reason. I saw this response to this sentiment posted by 'salivatingpanda' on here. It was buried in the comments but I think it deserves it's own post so here's what they said.
There is no real requirement that this short story be adapted to 4 seasons of 1 hour long episodes. This was decided by the show runners and network for whatever their reasons are. There are plenty of good shows that are only 1 or 2 seasons. This is an artificial and arbitrary limitation self imposed
They could have stuck to the core story as outlined in the books and expand on that in a logical and consistent way. Additionally, they could have added additional viewpoints and parallel story lines which complemented the core story. The decision to cut, merged and add to the core story was not required. Once again this was a decision made for whatever reason.
F&B is naturally 'inferior' to ASOIF considering one is an epic fantasy novel series and the other is an in-universe tie in historical fiction short story. The core story however is still pretty good and could have remained intact with minor alterations and build upon with additional stories and characters to flesh it out. There was no requirement to drastically change it.
Therefore, I don't agree with your statement that they had no choice when in fact the exact opposite is true. Everything that has occurred in this show was explicitly a choice made by someone for no good reason whatsoever. The only reason I can fathom why they made these choices are the same as GRRMs thoughts on the matter. These people think they know better and can do better by putting their own spin on the work of someone else.
I completely agree with these points and honestly I'm over making excuses for these show runners when there's shows out there with far less budget and no source material producing higher quality content. It's just sad. A waste of people's time and money.