[xorg loading intel driver on radeon system]

If it worked fine on xorg-1.18 , you could try updating xorg-kit to the 1.19-prime branch and see if that help. You update by setting it in /etc/ego.conf and then running ego sync

[ERROR: USE flag <flag> does not exist]

A lot of the tools from gentoolkit such as euse are broken with meta-repo due mostly to those tools hard-coding the gentoo repo and not respecting the alias setting. They are slowly being replaced with tools in ego. Please see the ego manpages for the latest tools available. 

[perl woes]

Hard to say other than that doesn't exist. Can't really test as all systems are on perl-5.24 since the switch to meta-repo. Can I ask why your still on 5.22? Are you still using 'stable' by chance?