For starters, I don't really class Shahriar Nafees Ahmed as a ODI player - good as he is, his team ain't ODI-class and I don't recognise a Bangladesh game as a ODI.
And Sarwan is quite possibly a better ODI player than Greenidge, yes - outrageous to you I know that might be, given that Greenidge is a better Test batsman than Sarwan can ever dream of being.
As for Clarke - if he continues on his merry way, he will indeed be a better batsman than Haynes (though there is a bit of a difference, Haynes being an opener and Clarke a middle-order player). Not yet, mind.
And you might want to consider a few things in your simplistic "a standard score than was... a standard score now is..."
1, plenty of games were 60-over affairs in those days (early ones in Australia were 40 8-ball-over games)
2, that means nothing to top-order batsmen's averages. They're still expected to score lots of runs and get a few not-outs. It's the lower-order batsmen who're going to have lower averages
3, who's to say less wickets didn't get burnt? If it's so hard to score at 3.5-an-over without losing your wicket, I don't know what it is.