I had similar experiences with the original SNES version of FF6j - often times you run into a certain pattern of monsters over and over. I had assumed at the time that I just had terrible luck, or that certain monsters were more frequent than others.
However, as it turns out, there's a method to this madness. Each fight is actually randomly selected from a preset group of 8 possible encounters. The encounters in each group are all fixed. You start the game with the group number set to 1, and it increments each time you fight a battle on the Veldt, to a maximum of 64. This counter also increases by 13 when you load your save.
You can only encounter monsters that you've fought before, so the game will skip over encounters that don't meet this requirement. That means that if you've fought very few monsters out of a group, the encounter pattern can be fairly repetitive.
A full list of the encounters and groups can be found on this page along with a description of the algorithm, which I used to research this answer.