Arthur Crabtree wrote: Smith in decline beats Root at his peak?
Comparing them without context is very misleading for a number reasons relating to circumstance. For a start, such a comparison ignores that both have a very marked difference in home v away averages, so the relative peaks and declines have margins before we consider one to have bettered the other - in the last 4 years they come out equal at 49 runs a piece.
But then you ask quantify those averages a little more. Smith played 70% of games against the top 3 ranked opponents Australia could play, Root played 48 percent. And Roots away form is proportional to both quality of opposition ranking + generic runs scored. For instance SL is the highest average place to bat for away bats, Roots averages best there. Second NZ, second also for Root. The trend goes all the way to elite sides where he performed badly in Australia, and under his own average vs India. So the expectation even using his own experience is that Smith's average is indicative of playing elite opponents in Australia, Root's away average is vastly inflated by easier opposition.
Then you ask, what is the current trend for away bats in Australia... the answer is, historically nightmarish. The average since 2021 is 21 runs a wicket for away teams, this is staggeringly low. In Australia's golden age peak in the 2000s, it was 29. Only India manage that in Australia recently, and that is still below historical averages. In England, runs have gone up for away teams, and all perform above expectations. Zimbabwe's performance in England is as good as the best anyone has managed in Australia, and only Ireland are worse than them. The obvious explanation is pitches. There isn't any bowling all-rounders smashing Gary Sobers record for 50s in a series happening, nor is there a record amount of overs or games going to day 5 happening.