As a regular driver from Liverpool to Portsmouth, I can assure you the drive is a nightmare. A lot of the journey is on the a34, not motorway, although not of a bad standard.
Yes, it can take just over 3 hours, but dont forget, coaches are limited to 60mph, which makes the journey more like 4 hours at best. However, due to congestion on the m6 and where the a34 crosses the m4 it can take literally double that at certain peak times. I know I must have done the route over 100 times in the past 10 years.
I was glad when flybe started LPL/SOU and latterly EZE. Stoke did the right thing in flying from EMA.