Using the Oogie Boogie card seems to help, but I never used it before.
As much as I'm not a fond of DDD, you are right. Prism is the best there is xD I almost never get Terra's earth powers since they're pretty weak, like you said. Terra is only powerful when hitting enemies plainly. Ventus' was a bit better but they didn't do much damage for me. Aqua's is much better, but using plain magic is much, much better in her story. Man, in the 2.5 version, they cut out Rhythm Mixer, and I was upset because I never played the original BBS.