Why is exFAT so slow on Mac? (reloaded)

The reason it is slow is that the implementation is not as optimized as it could have been.

A third party exFAT driver for macOS exists that you could try out. I doubt that it has better performance for. It is open-source and can be downloaded for free.

In order to format the disk so it can be used with better performance on both your Windows PC and your Mac, you can try a different file system. If you like exFAT and primarily have smaller files, you might be able to make do with FAT32 which is natively supported by both operating systems.

Alternatively you could format the drive as APFS, which is the native file system on macOS, and then install an APFS for Windows driver on your Windows PC. Note that the linked software is commercial and requires purchasing a license.

Yet another alternative is to format the drive as NTFS, which is the native file system on Windows, and then install an NTFS for macOS driver on your Mac. The NTFS driver that comes with macOS is read-only, so a separate driver is necessary in order to get read/write access. Note that the linked software is commercial and requires purchasing a license.