It's not rocket science! Saints approach is very simplistic and one which any team, at any level, can deploy. Fast line speed cuts down the thinking time and options of your opponents plus it is far easier to tackle a player, such as Walmsley, before they get into their stride. I can't understand why you would coach a team to have a defensive line that is static? You are inviting them to make yardage!
Coming out of their 20 is also predictable with 1, 2 or 5 taking the first two runs followed by Walmsley and their attack pays dividends because the likes of Roby and Lomax are playing against a retreating line of defence.
As for Cats, they were ok yesterday apart from their centres who were like turnstiles. I expect them to be much better when they have their first choice 17 fit and they are playing in the wet weather.