The 3/4 drop is not directly speed. As I said, it's accuracy, which will have an effect on speed. You can't press a button 15 times a second, but that doesn't matter - with an accuracy reduced, it won;t be pressed as many times as with 60fps, because the input update is not being done as frequently. The accuracy is ruined. Sadly, as you've noted, ff8 has many more things that require precise input compared to ff7 (which only had 3 reels). It's far worse when dealing with things that require precise timing to a display on screen (like Squall's trigger) , because that picture will be moving in larger increments at the same time as reduced input accuracy.
Look at this video I made and you'll see the biggest issue: