Aguero has scored six goals in as many league games this season and is just one strike away from joining Eric Brook as City's all-time leading goalscorer.
While Harry Kane (four goals) and Jamie Vardy (five) have also made good starts to the campaign, Arsenal great Henry said Aguero deserved most of the plaudits.
"The only one who is world class, or has been world class, is Aguero because of the longevity of what he has done in this league, year in and year out," the Frenchman told Sky Sports.
"He won the league here and he has been doing it the longest. You have to give him a bit of credit. I think sometimes we bypass Aguero like he didn't happen."
Aguero is a two-time winner of the Premier League and has netted at least 20 league goals in four of his six seasons.
Henry believes the likes of Lukaku, Kane and Morata will eventually get to Aguero's level.
"Lukaku has just arrived at Manchester United, he hasn't played long in the Champions League," he said.
"For Harry Kane, last season was short in the Champions League. It was short in the Europa League and the Euros.
"Morata was often off the bench at Madrid. He had a good year at Juve but he was playing with [Fernando] Llorente or [Carlos] Tevez.
"They will get there and we should be happy to have these players in our league."