TrueNAS was initially developed for big enterprise companies and later retrofitted to be also suitable for other groups as well. So, yes the system is more then suitable for business as well, the importance here is more the HW then the OS, to be able to handle the writes/reads for the amount of users.
And HexOS is just building on top of this already rock solid OS and makes it easier to setup and manage and backup. And since you still have TrueNAS underneath, you have the flexibility to do what you want in TrueNAS if you would require some more advanced features not yet available in HexOS.
Also Synology NAS are only working correctly nowadays with Synology drives which are just rebanded drives with a +10% pricetag