The mode of the MX is necessarily determined by its purpose (use case).
Therefore, I think it is best to avoid discussing the superiority or inferiority of each mode in a myopic way.
To benefit from the redundancy provided by DC-DC Failover, it must be a One Armed Concentrator.
Therefore, when redundant Primary and Secondary DCs are used in a corporate network, the DC side must use the
One Armed Concentrator.
Datacenter Redundancy (DC-DC Failover) Deployment Guide - Cisco Meraki
https://documentation.meraki.com/MX/Deployment_Guides/Datacenter_Redundancy_(DC-DC_Failover)_Deploym...
Routed Mode is suitable for accommodating Internet connections at branch offices.
To put it another way, One Armed Concentrator cannot accommodate Internet connections.