I have posted this before, but Scotland has 1/10 the population of England. It follows that the talent pool is 1/10 that of England. Therefore there will roughly be 9 good English players for every 1 Scottish one. However "Senior" Scottish football has only just less than the half the number of English clubs. It is inevitable that the standard of Scottish football will be much lower than that of "equivalent" clubs in England. I think it is absolutely right that the bottom half of the SPL is English third/fourth tier standard, the Scottish second tier is probably about conference level and so on.
Surely on that basis Wales and new Zealand should be crap at egg chasing?
There's also the point that Celtic are the only Scottish club who can pay anything like what an English player would consider reasonable wages. It follows that all Scottish players with any real talent will either play for Celtic or leave the country.