Everyone learns at different rates, some will take to it like a duck to water others won’t be much good for their entire lives with endless variances between the two extremes.
Those who take well to it are more likely to practice every second they can once they get a truck gig, others will do everything they can to avoid going backwards, the first group are likely to start with spotlessly clean windows and mirrors hedging advantage their way before they even start because they are interested in doing the job well, its not hard working out which group are going to be good at maneuvering in short order.
Regarding the test and the reversing test being seperate, does it really matter as the test reverse was a turn by numbers/markers farce anyway.
When i took my straight to class 1 back in the medievil period the course was two weeks, plenty of time to spend a whole day if needs be on the maneuvering pad, my instructor wasn’t happy until you could reverse the half the airfield assault course he laid out as well as drive through it forwards, there simply isn’t the time now on a standard course.
I’ll also point something else out that many will disagree with, maneuvering in manuals is much easier than in an auto due to the infinite control the driver has over the clutch itself irrespective of throttle control.