I think others have made really good points: 1) SOME amount of planning seems necessary these days with WDW, and 2) amount of planning can depend on how often you've been somewhere.
I'm a planner by nature. First couple of Disney trips were planned in great detail!! After that I eased up some, but dialed it back up after FP+ started. These days, I anchor our trips with 1) special events/experiences (eg Wild Africa Trek, Symphony in the Stars Dessert Party, etc.), 2) must-do NEW things since our last trip, then 3) ADRs and FP+. Also generally leave a block in the middle of the day for a hotel or other break with nothing scheduled.
Since we now know well what rides get busiest when, etc., etc., we don't go with a list of rides to do in order from 9-11am, or the like. We just make those calls on the fly based on what we know about typical wait times, what we've already done, exact wait times that day, etc.
Honestly, pretty similar with other trips in that if we've never been, I do a good deal of planning. If it's another trip to NYC, where we've been many times, I do less planning (but still find a cool new show, restaurant or museum and set that up).

That said, I think that for us, WDW will always require more planning than another been-there-many-times destination given constant changes, FP+, etc.