My challenge with giving a meaningful input to this thread is that I struggle to think of an author whose books series I have read and have read their stand alone stuff.
The closest I can come up with is Leigh Bardugo and this answer doesn’t really fit what you are asking for.
Her main series is the Shadow and Bone trilogy, her stand alone book that actually became a duology is The Six of Crows, which I enjoyed much more than the Shadow And Bone stuff. In fact I couldn’t finished the second book of Shadow and Bone.