A bit more to it than that.
The cap also acts as a noise supressor on voltage line into the RX
Ive actually seen this, Bluebird servo putting noise into the RX causing my Spektrum RX to restart. Cured with either a cap or descent servo

A Spectrum RX is good down to about APPROX 3v (ish), if the voltage will drops that far, a cap wont be enough to sort it.

If your esc's BEC output is only 1A, you need a external BEC if running hi-torqe servos, or cheapy servos that draw too much current.