It's VERY common for most brands of RTR's on the market to use bullet connectors between the ESC and motor, this is industry standard.

Racers know that adding extra connections will increase resistance and opportunity for points of failure as connectors go bad over time so most racers will opt to direct solder their wiring to the motor.

Back in the 90's most racers would direct solder their battery packs every charge cycle and never used connectors back then, granted the quality of connectors have drastically improved over the years.

There is no right/wrong/best method provided you are using quality components and regularly inspect/replace worn connectors.