The Pi 4's IO is not great, but the choice of SD card affects it a lot. Brand seems to have more of an impact than speed (or at least the stated speed of the card). Cheap knockoffs will absolutely kill performance. That's why Raspberry Pi started selling their own branded SD cards.

Using an external USB3 drive also helps but it's still pretty slow. I found it too slow to use as a SAMBA file server when connected over WiFi, even though it was hardly pushing the CPU or memory. It would regularly fail to transfer large files.

One of the main selling points of the Pi 5 is faster IO. I'd love to see something tiny and power-sipping like the Zero but with the enhanced IO of the Pi 5.

I am using a USB3 drive as a samba drive and it works fine, although I use it mostly for streaming video not to transfer large files.

My OS however is in the SD card which is Sandisk which I assumed was the good fair price brand.