The problem I had with the stock pump was that I sprung a leak and then didn't have time to look at it for a couple of weeks, by which time running the pump all the time had burned it out. A beefier pump means that you don't have to sort out a leak immediately, you can run with it for a couple of weeks until you get chance to look at it. I appreciate that, if you have the time to maintain the system correctly and sort out any leaks as and when they occur, the stock pump is fine. For me though a beefier pump and the leeway it gave me was better.
The L322 has been running for just over a week now with no issues, so it's already doing better than the P38 did. It's 6 years newer with 70,000 miles less on the clock though so that's to be expected