Larsson etc were significantly better than Christie, Macgregor and Forrest but that's not really the point. The point is you can still be a good player but play in Scotland and in some cases be capable of succeeding in epl.
Players from the Scottish Premiership may succeed in epl or may not depending on the club they choose /how they adapt to the league / how good they are like players from any other country. It's not linear. There is clear evidence that Scottish Premiership players CAN succeed in Epl, Van Dijk, Robertson, Wanyama, McGinn, McLean, Naismith, S Fletcher etc.