Yes, it is not unusual for a writer to get better at their craft over time. I know quite a few writers and most of them cringe at their own early works. And even if their writing didn't dramatically improve, their own knowledge of their characters and the setting does. So not at all unusual for a Book 2 to be better than Book 1.

And skipping over the "book is better than the movie" cliche, GoT hadn't fully taken off into the mega-hit, ultra high-budget blockbuster that we know it as in the first season or two. So yeah, probably were some corners being cut in early seasons that wouldn't have been if given the budget of seasons 6-7-8.