why SDWAN is successful in market rather than traditional routing & switching network or legacy one ?Please explain in simple words

in general, why asymmetric routing is not useful ?do it create slowness ?anyhow data is reaching to destination from source .Please share pros and cons of Asymmetric routing

How SDWAN router with single MPLS wan link will from control connection with VB,VS & VM as MPLS is peer to peer VPN 

If we convert any site TO SDWAN router then How SDWAN router will talk to Legacy sites .Please explain.

why do we need to login each switch individually in VPC in pair and we can get single login in VSS ?what is difference between VPC and fabric path ?how do we implement VPC in fabric Path ?