Exactly. It befell the same fate as the first Fullmetal Alchemist series, complete with an insane ending that was improvised and duct-taped to the end of an otherwise perfect series. At least they had enough wisdom to soft-reboot it, so they could finish the series the same way the manga did.

Dragonball Z also gets an honorable mention here, where the animation team was constantly at risk of getting ahead of the manga, so they had to build in LOTS of filler episodes to buy time.

Parts dedicated to Daenerys after Drogo's death early on were always stupid and boring. After her empowerement in sex scenes (rare W move), it then felt like a desert act of the second Diablo: sensless, useless filler stealing attention and screentime from other characters and events. It's easier to ignore now when you can watch episodes one after another, but when it was published one episode per week, seeing Daenerys was a major red flag. Undercooked ending wasn't as bad as her scenes dragging through all seasons.