Flip that around: would you expect that pilots flying a new aeroplane without any conversion training would be more likely to cause an accident.
It's a damning indictment of Boeing, and whichever authorities let them get away with it, that they pushed through an aircraft with a different pilot UI/UX knowing that pilots would then be under trained when using it: like someone said we train baristas better.
I've driven minibuses before and always ensure to get an hour of driving a new model before taking passengers.