This made me giggle. Like everything in the UK, the training has been pared back to the absolute minimum. The Piccadilly aims for
just 12 weeks from start to finish - although this often runs over. This includes 3 weeks theory at Ashfield house, 1 week of stock training, 1 week annual leave, 1 week hiking (walking around the depots and train crew accommodation), I think a few days SPAD mitigation, and then a load of time spent making the moves (into/out of depots, sidings, etc). That doesn't actually leave much time for actual driving.
Given my comment above, much of the actual learning is done after they have passed out. They tend to drive much slower, learn a lot in the mess rooms, and are prone to making more staff errors - not being in position, station overruns, or Passing Signals at Danger (SPADs). LU don't seem to make an association between the soaring SPAD rates and reduction in training time, and don't seem to worry about (well publicised) drivers accepting the wrong signal and ending up places they shouldn't really be.
Cross transfer train ops (from other lines) are expected to finish training within 8 weeks.
On a vaguely related note, the latest offer from LU for training on the new 24 stock is 'simulator training', with a
minimum of 7 stations physical on-train driving with an instructor.
I have almost zero knowledge of other lines, so hopefully others will be able to chip in.