Do NPCs not snipe? I ask as I do not know. I had the 7C Bi-Weave and some armor add ons. I can go back to it. How much does the extra weight affect the already bad turning?
NPCs used to snipe when 2.1 went live but that was patched out quickly. At that time I got killed multiple times with 85% hull left. These days I lose weapons when hit by missiles but I never lose thrusters, powerplant or FSD when attacked by NPCs. I did get a FSD malfunction when attacked by player iCourier, but fortunately that was when leaving a station so I just landed again and repaired. I still had around 50% hull left and thrusters were working fine.
As to the other question, there is no extra weight compared to a shield build. In fact, two small HRPs only weigh 16 tons and provide more than 500 extra armor + resistance when modded. PDTs are lighter and use less power than shield boosters, and I can run a smaller powerplant.
These are some of the overall stats of my modded T9:
0 shields, over 1300 armor
boost speed around 260 empty and 240 loaded, top speed without boost is around 150-160; this is with G5 clean drives
jump range around 26 Ly empty and 19 Ly loaded (512 tons of cargo)