I think? that maybe adding priority to the player to spawn at his OWN rally points would be a good consideration; if we want to give a selfish motivation for building them.
In this case The rally buff idea is simple and easy to implement; only locked behind the less played radio class; so it will appeal to players who already play the engineer/support mindset but will still be ignored by casuals.
I think its fine, as its the pros who want to support/carry the team anyhow, but basically lack the tools to do so. APCs are VERY good addition, maybe best in a long time, but I notice its still not enough.