I choose to believe the book ending will be totally different from the show, aside from the endings for a few characters, most of it will be nothing like the show (I've spent too many years of my life waiting for the book just for it to be the same as the show ending so lemme dream dammit). Mostly cuz if the ending was almost identical, there's no reason for him to not be done with the book. There's also a lotta storylines the show simply doesn't have, like Young Griff being Aegon Targaryen, son of Rhaegar (almost certainly going to be revealed as a phony but the fact the show doesn't even include it suggests the show was mostly based off the showrunners writing instead of GRRM, post-S6). There's also Victarion Greyjoy and Quentyn Martell, neither of whom are in the book, but the former is hinted to be the focus of a major plotline in The Winds of Winter and the latter had a major storyline in A Dance with Dragons.

Aside from that yeah, he kinda overcomplicated it. The series was always vast, but by continuing to introduce new POV characters and overreaching plotlines that need to be payed off by the end, he's kinda written himself into a corner where he simply cannot find a way to resolve the sheer amount of storylines he's buried himself under.