All valid your points.
The main reason is due to a migration from MCT brocade (similar to MC-Lag for juniper) to Juniper.
In the existing configuration I have MCT-brocade with VPLS, BGP, OSPF, VRRP running between the 2 MCT-Members.
Now, migrating from MCT-Brocade to MC-Lag or VC on MX i would like to keep the legacy design, especially the mpls due to a L3VPN already configured.
Not easy now to evaluate what is the less disruptive path to follow.
Both technologies, VC on MX or MC-Lag for Juniper have pro/drawback and for -n reasons they do not adapt properly to all the requirements.
e.g. MC-Lag active/active is good for having load-balancing for the traffic through the LAG but does not support mpls.
MC-Lag active/standby support mpls but not load-balancing for the traffic through the LAG.
VC on MX might fit but looks to me very complex in terms of defining the Class of service for VCP assumig there is a need to do it. No vrrp will be required in this case also, but at the same time I would need to change all the existing ospf peering, bgp. Also sw upgrade for VC on MX will create downtime and seems to me there is no way to avoid it.