The problem, as she goes:
- Everyone runs FSC constantly because it gives the most profit.
- FSC is too easy.
- The "final boss" can be defeated very easily by simply bringing Blitz Needle and Shivermist.
How do we solve this?
- Decrease FSC profits.
- Make the final area be more challenging. Give it a harder status than fire because fire is for babies.
- Make the final boss resistant to piercing damage.
More to the point, make FSC a T2 boss lair. In its place, bump up IMF to T3. The final lair will now be considerably less spammed because people hate IMF. Since the place is more about timing and puzzling than bringing the most overpowered gear possible, just derping in with a Blitz Needle will do little for you, IMF's boss is very resistant to both Blitz and Shivermist.
There is the matter of FSC having 5 floors while IMF only has 3. For starters, we remove the first floor from FSC. The one where you run north and glitch your way through gates and wheel launchers and people like to summon a GM because they botched up exploiting statues. Make it an IMF level instead, and FSC will simply start out at Charred Court. The IMF level will feature quicksilvers in place of oilers, retrodes and gremlins in place of zombies, and a couple of mecha knights in place of each Trojan. Shadow fire is replaced by shock pads, statue puzzles are replaced with switch-and-gate shenanigans which should require little effort to redesign. Alternatively, just keep the statue puzzles. Wheel launchers are of course replaced by rocket launchers. Instead of breaking them, you navigate your way behind them and press a switch to disable them.
Now IMF and FSC both have 4 floors going for them. You could add a fifth floor to IMF if you wish, but I don't think it's strictly necessary. So what'd we solve with this?
- FSC has less profits since it's a T2 lair. IMF probably wouldn't reach up to previous FSC standards either, making spamming the final area less attractive.
- The final lair now has shock instead of fire. There is no gunslinger and swordsman armour with naturally occuring shock resistance, nor is there for bombs until you get to IMF's Shadow Lair, which is basically the final Shadow Lair if you do this. As a result, non-class armours like Gray Feather and Mercurial would be more attractive. IMF is also filled with rockets that cannot be defeated through brute force. As a result, defensive armours would be of higher value there.
- The final boss is resistant to blitz, hazes and brandish explosions. Timing and experience would be the determining factor in defeating the final boss rather than relying on an cheat-bomb and/or absurdly overpowered weaponry.
I also believe that gremlin weaponry about to destroy Haven makes for a much better climax than fighting some guy who died in some war a thousand years ago.
Edit: Someone's going to bring up that Vana token items are 5* and Roarmie items are 2*. Just make the Vana token items 4* so you can't pass 5* Hall of Heroes with them and also they give less profits when sold. Noone cares about them. In sharp contrast, Pulsars and VT are very desirable items so it makes sense to get them from the final boss.
Not to say you are wrong but, I'm sure that FSC is filled with booty because of the large number of zombies in it. Nom Nom Nom, just a slash and they are basically pinatas filled with golden chocolate coins and small heart candies.
Reducing the profit earned from FSC can and will lead to a deflation rate, which though everyone might be supportive on, may not be such a good idea. Not to say inflation is good, but deflation is no better than inflation.