No pre-mapping doesn’t mean no oversight, fwiw.
The decisions taken with the plotting in TLJ will likely have been agreed with Kathleen Kennedy and/or other producers and execs at Lucasfilm and Disney.
(Eg, part of the reason Treverrow from IX was fired was because his script was bad.)
Don’t think this is any less valid way of running a long form narrative than Marvel’s more hands-on method, but obviously your mileage may vary on that.