TA3/Bowbreaker/Distant Def hard counters a +10 Merge/+Atk/Brave Bow+/Death Blow 3/Full Horse Buffed Brave Lyn. So, if you want to use him as a Brave Lyn Counter, he is pretty good!
As with other Low spd mages, Desperation/Brash Assault would do well. Swordbreaker doesn't help in the enemy phase(If you want to use QR Seal) unless you give him Close Counter.