Geoff Marsh performed very well between 1985/86 when he debuted and 1988/89. It was only from 1989 onwards, ironically the very time his team took a turn for the better, that his performances dropped off.
He was a fine servant during a difficult time but could not contribute enormously to the upturn. From 1989 onwards he averaged just 30, having averaged 39 up to the Pakistan tour of 1988/89.
Yes, up until the West Indies came to tour Australia in 1988/89 "Swampy" was clearly the first choice opener and I always felt he was capable of a regular big or decent score.
But the Windies were relentless with their attack of short pitched and short of a length bowling and, although courageous, he could never get going. (To be fair, his teammates couldn't really either). From then on more often than not, he just took the shine off the new ball.
Used to fend at the ball outside off stump too much, which was his downfall many times.
I still feel he was a batsman that underachieved a bit. He's someone I believe could have been as good as and/or statistically as good as Michael Atherton, averaging around 38 rather than 33.
The stereotype of him of course is that he had no shots. He actually started out for Western Australia in 1977 as more of a stroke maker and gradually as his career progressed he became more defensive and by the time he was well established in the Aust team he was considered as just a grafter.
He also suffered I believe, by playing on being the "team man" too much, to the detriment of his own game.
In fact, when he was dropped from the Aust test team in January 1992 he said something along the lines "I've never really been much of a stats man".
A previous post suggested that Marsh played a few too many test matches. But the team man ethic may have kept him there a bit longer. He wasn't really that bad for the time though. There was Haynes, Greenidge and Taylor who were better but then you had batsman like Wright, Athey and Ramiz Raja who weren't significantly better. Batsman didn't dominate like they do now.
Whether Shaun will be better? Hard to tell. Cricket is so different now to then that I may personally have difficulty deciding even if Shaun averages 45-50 in tests.