To me, the new software keyboard in tvOS is absolutely the biggest pain point and a major step back from the old password-entry grid on previous Apple TV models.
As ridiculous as it sounds, Apple has opted to put all the characters in a single line, two-row layout. This isn't just odd from a user experience standpoint, the new keyboard design in tvOS is a lot slower and clunkier to maneuver than the previous grid-style one.
And with the amount of passwords needing entering in third-party video apps, it's especially annoying and cumbersome. But as it turns out, there's a way to bring back the old password-entry grid to speed up typing those passwords.