The striker believes the two clubs have failed to attract stellar names for a number of years and have suffered as a result.
The Argentina international moved to Turin from Manchester City over the summer, but while the Bianconeri continue to compete for the best talent, the two Milan clubs have adopted a different approach in the transfer market.
The Rossoneri sold star names Zlatan Ibrahimovic and Thiago Silva to Paris Saint-Germain in 2012 and have sought to recruit younger players over proven big names, while Inter's ninth place finish last season and lack of European football means it has struggled to attract stellar players.
"Milan and Inter haven't bought major players for a number of years now. Without a strong team, you cannot do well," Tevez said in an interview with Corriere della Sera.
Tevez also spoke about Juve coach Antonio Conte and says he has adapted to life at the club more quickly than he ever imagined.
"Conte is a winner. If you want to win then you must get used to working hard like he does. My acclimatization to Juventus has been facilitated by the fact this team really is a team – on and off the field," he said.
However, one major disappointment for the Bianconeri was their failure to progress to the knockout stages of the Champions League – a competition Tevez has himself not scored in for four years.
"Our Champions League exit was a terrible blow to us all. We did not have the right nastiness in our opening matches," the 29-year-old said. "I think that things always happen for a reason. What happened in Istanbul - snow and playing the game on another day - it is not normal, but in the long run it will make sense."