I would greatly appreciate it if you stopped being rude. It's fine to have a difference of opinion, but calling someone a "snake oil salesman" and getting worked up over someone posting SC information in a SC thread isn't healthy for the rest of us. Thanks.
Source is anyone that has played SC for an extended period of time and does a lot of combat. As a hornet player, losing your wing or multiple thrusters is a usual combat thing and severely affects performance (having a top thruster fail on a super hornet usually means you need to respawn). It's possible you didn't notice it in the PU due to the awful framerate, but during the next free flight, try jumping into AC and see what happens when multiple parts of your ship fall off. Even losing a wing will make turning feel different. In third-person view, you'll see your thrusters firing at different angles in an attempt to balance the loss of mass. I'll float around on youtube and see if I can a good video showing this.
I also fly the Vanguard, which has 4 engines (2x primary, 2x backup), and losing one of the primary engines directly impacts flight performance. Losing both primary engines will make you useless in combat, and you'll need to limp home on the backups. If your forward thrusters fail, the ship is basically unflyable.
I even have this gfy of a sabre after everything's fallen off apart from the cockpit, and there's nothing left to control the ship:
https://gfycat.com/SmoggyOldfashionedGermanspitz
I'm not sure how to answer your RBC question as there's no easy way to prove that. Although back with the 2.0 release, CIG made it so top speed was based on the mass of your ship & power/weight ratio instead of static values. As much as losing a gun or using ammo would increase your top speed. This feature was disabled due to balance concerns in 2.2.