Hmm, new huge weapons would change things a little but let's look at the suggested changes one by one:
Firepower:
FDL - 4M, 1H. 6U
Python - 2M, 3L. 4U
Add in 2 more mediums and 2 more utility as suggested and it looks like this:
FDL - 4M, 1H. 6U
Python - 4M, 3L. 6U
Outcome: I'd trade 1 huge for 3 large any day of the week. Firepower it would absolutely kick the FDL's butt especially with a class 7 powerplant and distributor (both better than the FDL's 5 and 6 respectively).
Shields:
Since in your version they'd have the same utility I'm looking at pure shield value based on best shield available:
FDL - 5A, 468Mj
Python - 6A shields, 397Mj
Outcome: FDL wins by a decent amount especially when boosted 220% with 6 utilities (1,029 vs 872)
Armour:
Stock armour
FDL - 405
Python - 468
Outcome - Python wins, similar to shield value difference pre boosters.
Speed:
Lightest fit that allows boost:
http://coriolis.io/outfit/fer_de_lance/02D5A2D4D5D4D1C----------------.AwRhrSotho==.Aw18aQ==
http://coriolis.io/outfit/python/02A6A2D4D6D6D1C------------------.AwRj49RZckg=.Aw18eQ==
FDL - 302/406
Python - 267/349
Outcome: FDL wins significantly, proposed changes will increase the gap.
Overall summary of proposed ideas
Weapons are very OP on Pythons side.
A shield buff even by 30-40Mj will level the defence playing-field although it must be said most FDL users go for silent running builds these days.
Armour is already better than FDL, further buff widens gap making Python unquestionably better in defence.
Speed makes Python worse although given the current situation is so unbalanced a further drop shouldn't change anything.
Loss of internals does hurt but the FDL is already 70T vs 292T so even dropping 200T off the Pythons internal space and it still has the edge.
I think if you cut the weapon changes entirely it may be balanced. Even up the defence and manouvrability a bit and knock off the jump range.
Overall imo speed and jump range are the least important things in a fight so trying to argue them as an offset against the rest doesn't cut it for me personally. Internals does cut it but the FDL already suffers a lot compared with the Python. Speed is only needed to run and if you have the weapons and defence you suggest then you should not ever need to run.
Spent too much time here (work tomorrow

) and I feel like I've been a bit too negative. I hate knocking ideas without proposing alternatives but I honestly don't have the time to go into detail about the mid-high end ship I feel we need because you are 100% right there is a gap between the Python/FDL level and the Conda/Corvette/Cutter level that needs to be filled
Edit: I also feel like a big part of the problem was the FDL's powerplant buff, allowed the FDL to run top shields, thrusters and weapons without issue whereas before it had a deficiency somewhere that Python pilots could exploit. Perhaps the problem isn't in the Python but in it's opposition.