Simplifying:
1) older smbfs/smbmount had a "bug": they didn't support DFS (which Windows clients do, and Linux cifs client does) which is a critical feature of the protocol in multiple server environments
2) Windows does not support Unix Extensions
Samba server introduced a bug (long since fixed) which affects clients which support BOTH
Asking the kernel cifs client to always disable DFS support (ie without a mount option) to work around a bug in one server version would make things even worse because that would hurt accessing all of the servers that have working DFS support.
Simplifying:
1) older smbfs/smbmount had a "bug": they didn't support DFS (which Windows clients do, and Linux cifs client does) which is a critical feature of the protocol in multiple server environments
2) Windows does not support Unix Extensions
Samba server introduced a bug (long since fixed) which affects clients which support BOTH
Asking the kernel cifs client to always disable DFS support (ie without a mount option) to work around a bug in one server version would make things even worse because that would hurt accessing all of the servers that have working DFS support.