We are both getting bored doing the same exercises for and hour or two straight. )
First, I want to encourage you to keep learning, as you obviously are. I like seeing people moving forward, instead of saying, "My horse can't do that" and staying at low levels. Even if your horse NEVER floats like a Dutch Warmblood, it doesn't mean he can't develop his suppleness, strength, and get more beautiful!
The quote focuses on where I feel you've gone astray: dressage isn't just about doing exercises over and over. The exercises have a purpose. One does not usually work on them for so long, either, except in clinics, or in lessons--2 hours would be too much.
My advice is, first, to research the PURPOSE of each exercise you do. There are plenty of books around, and you can't go wrong with "Horse and Rider" by A. Podhajsky.
The next place of study would be the test sheets. Study the directives,which will help you learn WHY the movement is included. Once you start aiming for the "perfect score" you'll find even the simplest-sounding exercise can be quite complicated.
And of course, I hope you can still be able to take a lesson now and then. Otherwise, see if you can watch some. (That's what I do a LOT.