But that's the connection without the benefits of a high-frequency, high-quality Merseyrail service on the first bit.
Orrell to Wigan is 8 minutes, Pemberton to Wigan is 5. You're not going to speed that up much whatever trains you run, it's such a short distance.
As for frequency, it doesn't really matter how frequent trains to Wigan are if people are actually travelling to Manchester. For example, it takes me maybe 10 minutes longer to drive into Wigan, park, and go from there than it does to travel from Pemberton. As a direct service, it's tolerable, just about. But, add in a change, and going from Wigan is just a better option all round.
I'm all for increasing the frequency of services on both the Kirkby and Southport lines, don't get me wrong, but they need to be through services at least as far as Manchester and, right now, there just isn't the infrastructure to make that happen.