But there is.
Mini tamiyas weren't created to handle the currents of an upgraded gun. An OK tamiya can handle an OK basic gun fine, but crappy chinese ones definitely don't work properly with high amps.
If you shoot a dozen quick single shots and the connector gets warm, that means the contact area is too small for that current, there is loss. Deans have large contact area, no loss, that extra current can be used by the motor, if everything else can deliver that current.
So if you don't see improvement it can be because your tamiya was good enough to deliver the current or because there is an other bottleneck in the system.