Of course there's nothing wrong with approaching the modes in this way. It's not the only way, however.
Let's try an experiment. Record this progression on whatever device you have:
| C | D- | C | D- |
Repeat it several times.
Now rewind and improvise over it using nothing but the C major scale. Sounds good, right?
Try playing the E Phrygian mode over the same progression. Does it sound any different? Not really.
Try the same progression, but play a C major scale over the C chord, and a D Dorian scale over the D- chord. Any different yet? Well, you're emphasizing the roots of the chords as they change, but it still pretty much sounds like the same ol' key of C major, right?
Try it with any of the modes listed in the chart above.
It still sounds like the key of C major, doesn't it? That's because harmony affects how a melody is perceived. I don't care what you play over that progression, it will sound like C major every single time.
By the way, our example progression isn't modal harmony--it's a major "tonality". You hear tonality all the time in pop ballads, for instance. Usually, there is a progression of many different chords that occur in one or more keys.
Modal harmony is most often characterized by short, repetitive progressions, or vamps. Modal melodies usually don't stray far from the seven notes that naturally occur in the mode.
