Well, MicroSD cards go up to 250 MB/s. ~100 MB/s reads and 80 MB/s writes are typical for good new cards.

I guess eMMC goes up to 500 MB/s. I do wonder how much that fast eMMC chips cost, though.

A bit below 50 MB/s on RPi4 is actually pretty ok for most cases and whenever it's not, one can use an SSD over USB3.

Just need to make sure you have a good power supply and good quality cards, and SD card corruption is unlikely.