Clarke scored 3 double hundreds and a triple hundred. Beyond that his record, particularly in the last 5 years, is a series of failures interspersed with the odd century, about once every 10 outings.
Watson has been the far more consistent contributor with the bat, a contributor with the ball, and has had the balls to bat at 3.
In the last 10 innings, Clarke has scored more than 40 twice. Same as Watson. The previous 10 innings it was Clarke twice, versus Watson 4 times. The previous to that it was Clarke twice, versus Watson 3 times.
My belief is that they're both past it.
I certainly think it would be best for Australia if Clarke retired after this Ashes.
If all goes well he'll want to retire having just won the world cup and won our first series in England in 14 years.