The understanding I have is that if a Countries FTL is more restrictive in certain areas it can be imposed over the Sub Part Q.
In effect CAP371 will sit inside Sub Part Q and UK airlines will not see any significant gains. Those Countries who will loose out are those who have less rigid schemes, and those who have higher limits, i think Portugal and Spain have been mentioned.
This will still not see a level playing field but after 20 years or so of managing without a EU FTL do we really care anymore?.