This is exactly what I was thinking. Since people are disappointed in the writing, they have created this narrative in their minds that the actors don't like the writing either. In reality, the actors are likely referring to the story itself. So when they say it's "disappointing" etc. they are either referring to Dany going mad, or something that happens in the finale. I don't know anything about the show business, but I'd imagine publicly expressing dislike for the show you're in is not a great way to get hired in the future.

There is a clip where Peter Dinklage really sounded sarcastic when talking about DnD, and then he rolled his eyes. That was one where it did seem like he was saying the writing was bad, but these other ones people are pointing out don't feel that way to me.