I voted turnkey no regrets.
- i only use as a NAS / backup
- i run 90% of my VMs, containers etc on NUCs (I run one VM on the synology for proxmox backup server)
- i see the cost of the synology more about paying for their backup software than paying for the hardware
I loved migrating to 3 nucs from a 2015 synology, so think you are 100% correct. (It allowed me to use TB networking for a 26Gbe ceph network)