WSL2 is a VM based on a Windows virtual disk file (VHD). inside that VHD IO is quite fast , a couple degrees worse than native. /mnt/c is how you access your windows files, but it's slow like NFS (socket based). anything needing high IOPS will be dog slow e.g. compiles, file scanning, etc.

the rule of thumb without the newest features is to copy work to/from /mnt/c into $HOME as needed.