Of course, things have changed dramatically even in less than a couple of decades (far more, safe to say, than they changed in the previous 60 or 70 years). Of course, there is now more to teams becoming Test-class than there was in that of Zimbabwe, Sri Lanka and their predecessors. Though remember, of course, that Zimbabwe was for many years in cricketing terms part of South Africa. Likewise, Pakistan was simply a new political entity carved out of India.
But the thing that has not changed is that you cannot force cricket on those who do not wish to take it. Even the most enthusiastic, Kenya, Holland, Canada and (I say hesitently) USA currently have nowhere near the following to be challenging the big boys.
And I$C$C are doing far too much of this forcing for my liking, wasting money badly in doing so.