The first episode was an hour, but eps 2 and 3 were less, around 40-50 mins. (I haven't watched 4-8 yet.) So there was some loss of runtime, and I understand the need to change some things to make up that time. However, (and granted I'm only three eps in) I doesn't feel like the changes that were made were made strictly for runtime reasons.

Gran-Gran giving Katara the scroll instead of her stealing it, yeah, I see that being a time saver. The overall change in Katara's personality? Not so much.