What this thread is not about buffing the Panther. People just don't get this simply and I started feeling like I wasted my precious time trying to tell/explain something to 75% braindead community of this forum.
Your first post states "I came up with this idea: Make Panther 200 DMG with slower rate of fire (like Firefly). So :..."
If that is not a "Buff panther" then I truly am an idiot. You'd give it a huge boost to damage while only taking away 1.6 seconds on the reload. Paired with huge armour and HP (heavy tank-like stats), great speed, great penetration, that 200 damage would wreck all medium tanks. Nothing could stand against it's speed and survivability and hard hitting damage.
You are either proposing a buff to Panther or recoloring of firefly which is by itself the BS "more in line with..." cookie cutting.