You seem to be under the illusion that the South West is making these capacity issues up. You try boarding any peak time service and expect a seat out of Bristol/Cardiff/Exeter/Southampton etc. Heaven forbid if you get a 2 car 142 bouncing into Exeter Central at half 5...
The overcrowding issues in the North are seen as if you can get on the train and be squashed in the doorway at a weekday peak time or on a Saturday then the train isn't overcrowded, if people are left on the platform then it's overcrowded.
There is of course also the fact that the newest unit that First Great Western (west) operates is 1992 (ish), meanwhile in the North you have the 332 (?)
EMUs▸ in Leeds, 185s, 170s. But alas, the South always gets the new stock!!
Not a fair comparison.
The Northern area covers all local services (except Merseyrail) in three
UK▸ parliamentary regions and also extends in to a further two regions.
If you compare the North West based units with South West based units (both one parliamentary area) then Northern has around 60x142s, 40x150s, around 30x156s, 3x180s and 17x323s. With the exception of the 180s they were all built between 1984 and 1991. Merseyrail operate a fleet of trains built between 1978 and 1979.
The 185s may be fairly new but they are inferior to 170s and Voyagers that CrossCountry use on similar services in the Midlands and certainly not designed for 4 hours journeys. People doing 4 hours on them complain of a very sore bottom afterwards.
170s only run Manchester-Hull once an hour, so only make a brief appearance in the North West.
When most people in the North refer to the South getting all the new trains they are usually referring to the South East, but more recently the West Midlands as well.