Cash was a better player than his record would show or his personality would allow people to admit.
Despite having a very solid build and exceptional athleticism (his sprint times over 50 metres were in the elite category) he was very prone to injury and his career at the top level was, effectively over by 1989, at the age of 24. In those times he was healthy, he won Wimbledon, was runner-up in two Australian Opens (one on grass and one on hard court), reached the semi-final of the US Open, the quarters of the French, played the leading role in two Davis Cup wins and was twice runner-up in the Wimbledon doubles (semis of Aus and US Open doubles as well).
All up, just shy of the Edberg, Becker, McEnroe, Lendl, Connors, Wilander bracket BUT capable of beating any of them.
Actually, I think it's quite telling that, apart from McEnroe and Becker, he was good enough to beat all of those players, plus Mecir, Noah and Leconte, at either a major (French, Aus, Wimbledon, US) or the Masters. Great players, like those, might slip up at a lesser event but it takes a genuine talent to beat them when it matters most.