Quantity, yes, quality, no. Books 4 and 5 are fantastic, both reward rereads very well, and some of his best prose appears in book 5. Its prologue is the best in teh series, working on multiple levels.
Personally I think it’s a propensity toward laziness (based on his years of complaining how writing is such hard work) that was enabled once his finances took off and he became ‘comfortable’ that’s affecting the output. And possibly age, though I don’t like throwing that out because I don’t know of any actual supporting evidence and some people are anomalies and remain mentally quite sharp even into their last years.