There are several issues:
- the exFAT is designed to overcome the limitations of legacy FAT filesystem, however it coming with a high cost - the block size is big.
- it doesn’t have a journal, so in a long run there is a higher chance to lose the data.
You can read more there:
And yes, the block size is an issue in this exact case, but I would take into consideration the durability too. It’s more important to Storage Node Operator though, since the network have an additional 79 pieces (except yours), when only 29 is needed to reconstruct the file.