Why are Squall and Yuffie so easy to beat

[PuPu]

I guess I'm not at X-mashing as I thought, since they usually beat me in about 10 seconds when I try to X-Mash in that battle.

Though it might be more likely to win by X-mashing on Normal or Easy Mode.

Mode matters not.

I use Limit/s to kick them in their pants.

You can't, since in that fight you don't get Donald or Goofy, meaning no Drives, Limits, or Summons.

Unless you used Trinity Limit, then ran around the arena waiting for your MP to restore so you can use it again until you win?