Despite increased competition, the Silver Arrows have again cruised to the Constructors' Championship and having won nine races so far this season, and Lewis Hamilton could seal the individual crown at this weekend's United States GP.
The situation has led to criticism of the sport, with experts bemoaning the fact it has become somewhat predictable.
Mansell drove in one of F1's most competitive eras, going up against the likes of Ayrton Senna, Alain Prost and Nelson Piquet before finally winning the title in 1992.
The 62-year-old admits Hamilton has had it easy this season and says the sport needs Ferrari to make significant improvements to challenge Mercedes heading into 2016.
He told La Gazzetta dello Sport: "He (Hamilton) has a great team, wins with little trouble and that is why everything is easy for him.
"More competition, and a Ferrari that is closer in performance to Mercedes, is needed, so that things would be like my era when Senna Prost, Piquet and I were always fighting."