England head coach Eddie Jones said the tourists' series win over Australia was "tougher" than their victory against the Wallabies in 2016.
Five years earlier, arriving off the back of a Grand Slam win at the Six Nations, England completed a series whitewash in Australia.
"This was tougher than 2016," said Jones.
"We had to fight like anything today, they were always going to throw it around so we had to defend well."
England opened their Australia tour by falling to a dismal 30-28 defeat against a 14-man Wallabies side in Perth.
But they produced an aggressive and resilient display to beat their hosts 25-17 in the second Test in Brisbane, to ensure their match in Sydney would be a series decider.
"When you fight like that and win a game like that, it's a real achievement but all the credit goes to the leadership group," added Jones.
"The result is always important but the development of the team, especially now when we're in the last 12 months of this World Cup cycle, it was crucial we got it right."
Come-from-behind win 'sweeter' says Steward
England started slowly at the Sydney Cricket Ground, finding themselves 10-3 adrift before Freddie Steward crossed on the stroke of half-time to give Jones' side an 11-10 lead at the break.
Marcus Smith ran in from long range after the restart before England held on despite a late fightback from the hosts.
"To come back from 1-0 down and win 2-1 makes it even sweeter, particularly when the boys dug in for 20-odd phases at the end," try-scorer Steward, making his first appearance for England in the southern hemisphere, told BBC Rugby Union Weekly.
"To see the boys go to the well like that gives you so much energy and brings everyone closer together.
"To win after a set like that is brilliant."
'We're tighter as a group'
England came into the series looking to bounce back from a torrid 2022 Six Nations campaign in which they claimed just two victories.
Their win last week in Perth ended a run of four consecutive defeats and five losses from their past seven matches.
"There have been signs it is coming together, which is exciting," added Steward.
"We can look forward to the autumn and Tests against New Zealand and South Africa and we are building nicely.
"It has been a brilliant tour for us, we are a tighter group and the rugby is better because of that.
"The wins that aren't pretty, where you really have to go to the depths to get a result, mean more I think, when you come of the field after being battered and bruised and have given 110%.
"They are sweeter than when you steamroll teams 30-0."