Umm holy spamming is extremely easy against mages, and slide hazard rips through all of her bp attacks, so shes very easy to combo
Terra holy spams herself and ice can be used to block holy (whirls up like a shield in front of her, I often use it to block most incoming missles) Terra does struggle more with golbez than Bartz does however, since Bartz'es ground game is vastly superior to Terra's.
Holy is pretty easy to dodge away from anyway if you have omni-dash and extended dodge (dash through the first pass then dodge away from the turn around) I can go an entire fight against holy spammers and not get hit once, If Bartz can close down the distance however Windshear > Tornado (triggers quicker and can cut through the first spin)
Bartz is decent at range, but trying to out-fight a ranged character in there element is not going to work, better off trying to shut them down and keeping them at mid-close range where bartz can deal with them more comfortably.
Remember Bartz is a jack of all trades character, master of none. Trying to outcast a caster isnt neccessarly going to work against a caster that knows what there doing, holy spamming is definatley a bad idea when it comes to to likes of Kuja as you'll just be a sitting duck for his ultima and remote flares, bartz is no doubt a tricky character to beat, but I'd say hes not the hardest to beat, that pretty much belongs to Golbez and Ex-Mode Gabranth.