that was my gut reaction. but from my limited experience with creatives in showbiz, i'm more willing to believe that

1) D&D knew that 2 shortened seasons to end it was going to be extremely difficult to pull off

2) Absolutely believed they nailed it when they sent the tape off to HBO

These guys certainly expected to see headlines like "Game of Thrones is the most disappointing show ever" on Reddit or ASOIAF fan sites, because that element has always been there. But not on Esquire, Vanity Fair, etc. Mainstream press has been almost universally fawning over the entire series, mainly started to turn when season 7 aired after they were already deep in production for season 8. They truly believed they had a blockbuster hit that would be remembered by the masses as the most exciting finale ever.

Showrunners/directors don't typically do a shitty job on purpose. They can just be hugely narcissistic and believe that whatever they put out is good, especially when they've been receiving bonuses, Emmy's, and job offers over their work.