They would be able to offer more choice! They would more likely generate more pax and compliment each other!
AF/KLM don't see it like that.
AF used to have three daily rotations from BRS to CDG but once the merger with KLM came along they pulled their Paris flights leaving the five KLM BRS-AMS rotations to deal with the merged airline's long distance pax.
There were plenty of 'local' BRS-CDG pax because BACx (who used to compete with AF) stepped in and increased their own daily rotations to five once AF left, but clearly AF are not interested in short haul traffic from smaller UK regional airports, and if they aren't interested at BRS with rising 5 million annual pax would HUY be any more likely to find their favour?