Robert Jordan dragged out a series for commercial reasons and altered a major storyline when fans guessed it, leading to an uneven story, and then died before he could finish (due to his own slowing down of the series), leading to what most would consider was a lackluster (at best) ending.
Georgerr Martin can't seem to write anymore and let HBO finish his story for him in a slipshod and rushed fashion, poorly handling pacing and resolution for multiple story lines. He's also not in good health, doesn't seem interested in finishing the books at all and will likely die before finishing.
Which author let down his readers more?
So in sum my argument is better to leave things unfinished but provide a great ride, than a subpar product which feels like a waste of time *.
*We live in a world of culture abundance, so wasted is not just a lost of the time you invested, but is also a second loss you could have been doing something else during that time, such as another culture product, but also fun awesome "base" things like eating, drinking, sleeping, hanging with friends, cuddling, etc.
** You can reverse my argument that an unfinished series that you invested in is a waste of time, but I disagree. Good series change you via reading and thus this inward journey in my opinion is more important of what ends up doing what at the end of the story. But hey this is the realm of opinion so feel free to disagree. (In the end? Nothing ends, Adrian. Nothing ever ends. [unsettling disappearance into vapor] [vanity is vapor, just like Cain is vapor, it is all breath / "hebel." )
-----
I consider Game of Thrones the TV show a separate thing from ASOIAF, but season 8 (I stop watching with season 5, but I watched a third of Season 8,) is part of my argument. Book 7 of 10 of RJ is very similar to Season 8 of Game of Thrones which I witnessed, even though that TV show is adding a ++ to the badness scale.
And remember internet people ruin everything for Game of Thrones would not have been made without the Shibboleth of R+L=J in 2006. Martin had one thing to determine if a person who wanted to do the adaption was a friend or foe, if they could "get his work" and not make a mockery of it, and it was the Shibboleth that was bloody obvious by the first book. Well before that Santa Monica Boulevard "BRUNCH D&D went on internet boards like this one to prepare and there they learned the secret Shibboleth for fans were speculating about R+L=J after book 4 came out with AFFC (2005 and 2006.)