Bit flip probability is inversely proportional to density of the storage media so denser might have you run into issues. Also theres no point on building a recorder that's 10x larger than what you need if you're going to be limited by downlink availability. You could probably get away with all those SD cards in LEO though for a short missions, JWST falls into the category of missions where the price of that storage medium is going to be a rounding error vs the price it would incur if it randomly failed during qualification.