There are these fundamental problems with FL.
It's easier on maps that don't have many jumps, notes clump up ETC. and harder on maps that are based on jump. Nevertheless grant the same amount of score multiplication. - I know that pp does take that into account
slightly (I think this will soon be confronted, as ppy is still have a hard time dealing with scaling base on pattern and such and there isn't a pressing need to pay attention to FL yet. But still I'm dreaming of a future where HDFL is as viable as HDHR or HDDT (as so is some others like:
This guy)
FL is pretty tough. Not everyone just walks in on a >800 combo (the number is just for show, I'm just trying to say a long map) song and decides: "Yeah imma HDFL that to get mah juicy pp". It will take hundreds even thousands of replay, luck and brain power to achieve a somewhat pp-worthy play. FL in my opinion is underrated as it require a lot of dedication, mental stability and extreme memorization on hard (HARD) song. Nevertheless doesn't improve one's reaction skill, speed ETC. (which is crucial to improve oneself in osu).
But still if we buff FL then your pp (gained from playing FL) won't show how good you are at osu in general which will then require a separated ranking system for memorization skill ETC. (very troublesome if you ask me and does not guaranteed people's attention to the mod itself) but if we don't it will never be worth (unless you are aiming for a flashy play or #1 - no pun intended).
This suggestion is something of a cry of a problem which is openly ignored by most. (or at least, overshadowed by the DT, HR war)
Also, why not just remove the blackened area and substitute with a ring around the cursor and make the notes outside of the ring invisible? (It's still the same as FL but less strain on memory as you can now rely on the background picture to memorize the location of the notes easier and aim better but still force you to memorize the map anyway - minor buff to FL anyone? - will then have to change FL to something else because of the drastic change in appearance)
Man, balancing is hard.
Then there is also problem with easy mod lol... life is tough