Guard Counter is used in normal battles too and it is barely much of a trick.
However you even go as for to get an EX-guard? My characters all have EX builds and the only time I go into EX mode is when I fight in the Blackjack course in Duel Colliseum.
When farming these strats are just godlike:
Onion Knight EX mode build
Emperor Starfall spam
Warrior of Light EX mode build
Kuja EX mode build (if you can do the HP attacks correctly)
Zidane (Yeah, just Zidane)
Cloud of Darkness spamming 0-form particle beam.
Squall Beat Fang spam
Onion Knight Lai Strike build
Sephiroth Lai Strike build
Warrior of Light EX and Lai strike build
Those are the ones I use at least.
Well all the abilities is used for the character, I too play around since none of the A.I is challenging anymore. When I stop doing Bravery to HP chain and instead just doing Bravery to Bravery chain just for the fight to get longer I know I've already roflstomped the opponent.