Yes, it's always a question about total weight, ready to fly.
You can say that when a motor is rated "from- to-", it means that below the "from-" weight, this motor is considered to be overkill, (more like a motor with an airplane, than an airplane with a motor, so to speak...) but the more you approach the "to-" weight, the more sluggish and underpowered the model model will perform. Then again, this is also depending on what type of airplane you have. With the same motor, a trainer with lots of wing area and can fly slower and better than a scale model with less wing area even though the models weigh the same. This is because of wing loading; total weight divided by wing area. The higher the wing loading, the more speed (=more power) the plane needs to stay in the air. The wing profile (lift) is also a part of the equation.
Hope this helps you, may all your landings be in one piece!

Brg
Pops