ALthough a cap >100uF is recommended by one supplier and perhaps others suggested 1000 uF, no one suggested switching that cap from the same uC.
The cap must be before the switch close to the stripleds to reduce the chance of transient errors in the logic.
General purpose Caps have an ESR of 1~2 Ohms at 100uF and low ESR caps will be 1/10th of that or less. So your 5V rail will spike low from the surge current I=V+/ESR, when switching the cap.
But you need the cap close to the stripleds, to decouple the MOSFET drivers on each chip, so your added "master ON" MOSFET MUST ALSO be close to the power connector, but after the cap.
You ought to understand Ohm's Law by now and fast switching a large cap will result in a surge current determined by V/ESR. THis means the uC board would need 10 of the same caps in equivalent C and 1/10th ESR to just reduce the transient drop to 0.5V or 10%.
precautions included from POLOLU website are
Warning: The WS2812B seems to be more sensitive than the TM1804 on our original LED strips. We recommend taking several precautions to protect it:
Connect a capacitor of at least 100 μF between the ground and power lines on the power input.
Avoiding making or changing connections while the circuit is powered.
Minimize the length of the wires connecting your microcontroller to the LED strip.
Follow generally good engineering practices, such as taking precautions against electrostatic discharge (ESD).
Consider adding a 100 Ω to 500 Ω resistor between your microcontroller’s data output and the LED strip to reduce the noise on that line.
If the strip does get damaged, it is often just the first LED that is broken; in such cases, cutting off this first segment and resoldering the connector to the second segment brings the strip back to life.
Consider the gate has a TVS for ESD protection if you intend to have loose connectors.