A Deans or bullet connector is intended to be soldered but the typical servo and battery connectors are not. They are intended to be crimped. A proper crimp works very well.

The key is to do it right, using the correct tool. I see a lot of people (usually outside of RC) try to use a dollar store crimper/stripper tool and wonder why their results are so bad.

Regardless of whether somethign is soldered, crimped, or whatever take the time to get it right and it will be much more reliable.