He was just ahead of its time in terms of grind and realism. I remember one of the first times gregtech was introduced to the mainstream was with the Mindcrack FTB modpack, most people hated it because they were used to being able to unlock ore doubling (with the ic2 macerator) within the first 20 minutes of a new world. He increased the difficulty by making the recipe need diamond cutting heads instead of a ton of iron. As you said he did this by modifying another mod's recipe (in this example ic2) which was frowned upon at the time.

In a sense, he created expert mode modpacks before they were a thing, where it is common and expected to modify recipes from multiple mods to make a more interconnected recipe chain.