You're adding speed ("going faster").
You're adding a 200% of speed, which is twice the nominal speed (the 100%). Given the nominal speed is 1x and you're adding 2x, you end with triple the magnitude of the original nominal speed.
People will rail about them using it wrong but it's pretty useless when you have to basically guess whether people subscribe to your definition of "right" before you can understand something.
I'm using the exact same terminology, so splitting hairs on phrasing isn't going to work for me.
After some clever engineering, it now runs 50% faster. Its speed is now 100% (baseline) + 50% (improvement) = 150% of 1 m/s (original speed) = 1.5 * 1 m/s = 1.5 m/s
The budget option runs 20% slower than the original model. Its speed is 100% (baseline) - 20% (derating) = 80% * 1 m/s (original speed) = 0.8 m/s.