if you move the show call into EVERY_N call
output get much more smooth.
I guess that the high refresh rate of leds causes the flicker.

And as long you do not change the LEDs there is no need for a show call.

results in:

void loop () {
EVERY_N_MILLISECONDS(thisdelay) { // FastLED based non-blocking delay to update/display the sequence.
ripple();
show_at_max_brightness_for_power();
}

} // loop()