Tier 1
Australia
India
England
Tier 2
West Indies
New Zealand
Pakistan
Tier 3
South Africa
Sri Lanka
Let's test this (incredibly unscientifically) by listing the top 5 middle-order batsmen (why no openers? that tends to be much more era-dependent than country-dependent me thinks) of each country. = means average remains about the same in CW eyes; − means average worsens significantly, + means average increases significantly
Aus: Bradman (=), Ponting (=), Border (+), G Chappell (−), Smith (=); overall =
Ind: Tendulkar (=), Dravid (−), Kohli (?), Laxman (+=), Hazare (−=); overall =
Eng: Hammond (−), Barrington (−), Compton (=), Root (+=), May (+); overall −=
WI: Sobers (+), Viv (+), Lara (+), Headley (−), Weekes/Walcott/Chanderpaul (−); overall +
NZ: Kane (−=), Crowe (+), Taylor (+), Fleming (+=), Jones (−=); overall +
Pak: Younis (−=), Javed (−=), Inzamam (=), Yousuf (−), Zaheer (+); overall −
SA: Kallis (−=), Pollock (−), Nourse (=), de Villiers (−=), Amla (+=); overall −
SL: Sanga (−=), Jaya (−), Aravinda (+), Mathews (?), Samaraweera (−−−); overall −
There is some national bias here for sure but it's much less than any other cricket forum you'll find. And don't try to twist these results into supporting your hypothesis; you literally said Tier 2 players' averages don't change. There is one = player in that group. One.