Game of Thrones has taken out the Night King and his army of the dead... but surprisingly, Bran Stark survived, and that creates a problem, because he's now so overpowered that he throws everything off balance. 'The Long Night' saw the Night King come to Winterfell, and while fans were predicting all kinds of twists (that he wouldn't actually be at Winterfell, but King's Landing, or that Bran would become the Night King), the battle actually played out in a fairly straightforward way. A handful of characters died, Theon sacrificed himself for Bran, there was a phenomenal dragon battle, and just when all hope seemed lost, the Night King was killed. Essentially the only major twist was that there was no huge Azor Ahai moment, and instead, Arya was the one to take down the Night King in the end.
On one hand, fans are breathing a sigh of relief that the final battle is going to be more of what Game of Thrones does best - political intrigue rather than zombie hordes. On the other, however, leaving Bran alive creates something of a problem. This means that rather than having humans duking it out over the throne, Team Winterfell has a ridiculous advantage - they have two magical creatures (the dragons), and a magical greenseer whose powers seem increasingly unlimited. That's hardly going to be a fair fight - which means it's not going to be a particularly compelling one, unless Bran gets killed off (or depowered) very soon.
Bran As The Three-Eyed Raven Is Completely Overpowered
Bran, as the Three-Eyed Raven, has essentially become the Superman of Game of Thrones: he has a huge variety of powers, and they seem to be near-unlimited. Originally, Bran couldn't do a whole lot other than warg into various animals in his dreams. However, as time has gone on and thanks to his training in the cave of the Three-Eyed Raven, Bran has more powers than the average comic book hero.
He can see everything that has ever happened in Westeros, can see things that are happening now, and has visions of the future. These visions also seem to be extremely clear - he knew, for example, that Jaime was coming to Winterfell, and that Arya would be the one to kill the Night King, and that she would need the Catspaw Dagger to do it (either that, or he is simply an extremely lucky guesser).
In addition to simply having visions, he's also been shown to be able to interact with the things he sees - not only in the heartbreaking Hodor scene, but when he called out his father's name while watching him at the Tower of Joy (and Ned turned around as though he heard it), as well as in his vision of the Night King where he was 'marked'. These are significantly more than simple prophetic dreams.
He can also still warg, of course, and it seems that his warging abilities have become incredibly strong. In 'The Long Night' he was seen warging into an entire flock of birds, and he has shown in the past that he can warg into and control anything - even humans. Presumably, he will even be able to warg into a dragon, if he feels like it. His powers aren't just strong, either. They are growing exponentially, and seemingly without any real cause other than to help forward the plot (as with his gift of the dagger to Arya).
Greensight In Game of Thrones Is Significantly More Powerful Than In The Books
It's also worth noting that Bran's gifts seem to outstrip the powers that a greenseer has in the lore of A Song Of Ice And Fire. While the abilities of greenseers are mixed in with myth and legend, they are definitely not as overpowered as Bran seems to be in the show.
The books describe greenseer visions as more vague, and difficult to interpret. They are closer to the kinds of visions that Melisandre would have in her flames, or that Daenerys had in the House of the Undying. They may be helpful, but they are also very easy to misunderstand. Jojen Reed, was much closer to the book version of a greenseer, able to get a general sense of where to go or what would happen. The books also create more of a connection between the greenseers and the weirwood trees; in A Song Of Ice And Fire lore, Bran should be able to see through the eyes of the other trees - but in the series, it seems that while he likes to hang out in the weirwoods, he is capable of using his powers from anywhere, and to see anywhere, not just what the faces on the trees would see.
Keeping Bran Alive Kills The Dramatic Tension
The biggest issue with the overpowered Bran/Three-Eyed Raven is that, very simply, it would seem to make it impossible for his side to lose the upcoming war. The remaining three episodes of the series will be (presumably) focusing on the battle between Jon/Daenerys and Cersei - or perhaps between all three, should Jon and Daenerys split following the revelation that Jon is Aegon Targaryen. Whether Jon and Daenerys continue to work together or not, Bran's survival puts Cersei at a ridiculous disadvantage.
Daenerys has two dragons (as it was confirmed by the trailer for the next episode that Rhaegal is alive and well), and Bran has the magical ability to see everything that is happening or will happen. The Golden Company is simply no match against so much magic, which makes it impossible for Team Winterfell to lose. Game of Thrones thrives on dramatic tension and plot twists as the characters attempt to outmaneuver each other - if one side has a magical kid who is constantly revealing what the other side is up to, it destroys that tension. Few fans may actually want to see Cersei win, but to have a truly compelling final season, she needs to at least stand a chance.
Bran Needs To Die (Or Go Back North)
Like Melisandre, Bran has served his purpose in stopping the Night King - so now he needs to disappear. Keeping him around serves no purpose except to tip the scales ridiculously in favor of Jon and Daenerys, and there's not a whole lot more to be added to his character arc... or that he can add to the arcs of others, now that he has forgiven Theon and reunited with Jaime, and told Jon of his true heritage. There's also no real place for him anymore; Bran as Lord of Winterfell would make no sense, because he's completely checked out as the Three-Eyed Raven, and if any Stark should be running things, it's clearly Sansa. His family would never kick him out of Winterfell, but the idea of Bran simply sitting out the rest of his days by the weirwood tree, being slightly strange, seems like a deeply unsatisfying end to his story.
Instead, Bran should remove himself from the Game, by heading back up North or somewhere underground where he can completely become the Three-Eyed Raven, or someone else should take him out. Bran's death could be a fantastic way to throw things into chaos, too, depending on how he dies. Should Daenerys kill him, in order to prevent anyone finding out about Jon/Aegon, it would be a brilliant moment that turns Daenerys into the final villain and drives a permanent wedge between her and Jon. Perhaps Jaime or Tyrion could betray their current allies, and go back to House Lannister having killed Bran to save their sister. At this point, having anyone at Winterfell take out Bran would be a huge dramatic twist that would change everything, and remove the Three-Eyed Superman of Westeros in order to level the playing field, and give everyone the dramatic ending that they deserve.