the simplest solution for a game being to easy is to just not level up anything beyond what would get leveled within the normal course of the storyline... in FFVII that means don't wander the world map, don't do side quests that don't progress the story, the only exception is if you wanna fight Emerald and Ruby as they are a true challenge, but if you defeat them then Sephiroth will seem too easy defeating the whole process of not leveling beyond the story...